What's new

• 20 Must-know Advanced JavaScript Interview Questions for Experienced Engineers

  Get ready for your senior front end engineer role with these top 20 advanced JavaScript interview questions and answers, curated by ex-interviewers for experienced developers.

  Level

  Advanced

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  15 min read

  Nov 2, 2024

  Copy link

  Share

  ---

  JavaScript interviews for experienced engineers demand more than just a basic understanding of syntax and concepts. They require a deep dive into advanced topics that demonstrate your ability to solve complex problems and architect robust solutions. Whether you're aiming to advance your career or secure a new role, mastering these 20 advanced JavaScript interview questions will not only enhance your technical prowess but also set you apart from others.

  1. Explain why the following doesn't work as an IIFE: function foo(){ }();. What needs to be changed to properly make it an IIFE?

  IIFE stands for Immediately Invoked Function Expressions. The JavaScript parser reads function foo(){ }(); as function foo(){ } and ();, where the former is a function declaration and the latter is an attempt at calling a function without a name. This results in a SyntaxError.

  To fix this, wrap the function in parentheses: (function foo(){ })(). This turns it into a function expression, allowing it to be executed immediately.

  2. What are iterators and generators in JavaScript and what are they used for?

  In JavaScript, iterators and generators are powerful tools for managing sequences of data and controlling the flow of execution in a more flexible way.

  Iterators

  Iterators are objects that define a sequence and provide a next() method to access the next value in the sequence. They are used to iterate over data structures like arrays, strings, and custom objects.

  Creating a custom iterator for a range of numbers

  In JavaScript, we can provide a default implementation for iterator by implementing [Symbol.iterator]() in any custom object.

  class Range {
    constructor(start, end) {
      this.start = start;
      this.end = end;
    }
  
    [Symbol.iterator]() {
      let current = this.start;
      const end = this.end;
      return {
        next() {
          if (current <= end) {
            return { value: current++, done: false };
          } else
            return { value: undefined, done: true };
          }
        },
      };
    }
  }
  
  const range = new Range(1, 3);
  for (const number of range) {
    console.log(number); // 1, 2, 3
  }

  Generators

  Generators are a special kind of function that can pause and resume their execution, allowing them to generate a sequence of values on-the-fly. They are commonly used to create iterators but have other applications as well.

  Creating an iterator using a generator function

  We can rewrite our Range example to use a generator function:

  class Range {
    constructor(start, end) {
      this.start = start;
      this.end = end;
    }
  
    *[Symbol.iterator]() {
      let current = this.start;
      while (current <= this.end) {
        yield current++;
      }
    }
  }
  
  const range = new Range(1, 3);
  for (const number of range) {
    console.log(number); // 1, 2, 3
  }

  Iterating over data streams

  Generators are well-suited for iterating over data streams, such as fetching data from an API or reading files.

  function* fetchDataInBatches(url, batchSize = 10) {
    let startIndex = 0;
    while (true) {
      const response = await fetch(`${url}?start=${startIndex}&limit=${batchSize}`);
      const data = await response.json();
      if (data.length === 0) break;
      yield data;
      startIndex += batchSize;
    }
  }
  
  const dataGenerator = fetchDataInBatches('https://api.example.com/data');
  for await (const batch of dataGenerator) {
    console.log(batch);
  }

  3. What are JavaScript object property flags and descriptors?

  Property flags and descriptors in JavaScript manage how object properties behave, allowing control over property access, modification, and inheritance.

  Property Flags

  Property flags are defined using Object.defineProperty(). Key flags include:

  • writable: Can the property be written to? Default is true.
  • enumerable: Is the property enumerable? Default is true.
  • configurable: Can the property be deleted or reconfigured? Default is true.

  Property Descriptors

  Property descriptors provide detailed information about a property, including its value and flags. Use Object.getOwnPropertyDescriptor() to retrieve and Object.defineProperty() to set them.

  Example:

  let user = { name: 'John Doe' };
  let descriptor = Object.getOwnPropertyDescriptor(user, 'name');
  console.log(descriptor); // {value: "John Doe", writable: true, enumerable: true, configurable: true}

  Manipulating Property Flags

  • writable: Controls if a property can be written to. If false, writing fails silently in non-strict mode and throws TypeError in strict mode.

    const obj = {};
    Object.defineProperty(obj, 'name', { writable: false, value: 'John Doe' });
    console.log(obj.name); // John Doe
    obj.name = 'Jane Doe'; // TypeError in strict mode

  • enumerable: Controls if a property is visible in for...in loops.

    const obj = {};
    Object.defineProperty(obj, 'name', {
      enumerable: false,
      value: 'John Doe',
    });
    for (const prop in obj) console.log(prop); // No output

  • configurable: Controls if a property can be deleted or reconfigured. If false, deleting or altering fails silently in non-strict mode and throws TypeError in strict mode.

    const obj = {};
    Object.defineProperty(obj, 'name', {
      configurable: false,
      value: 'John Doe',
    });
    delete obj.name; // TypeError in strict mode

  4. What are JavaScript polyfills for?

  Polyfills are scripts that enable modern JavaScript features in older browsers that lack support, allowing developers to use the latest language features while maintaining compatibility.

  How Polyfills Work

  Polyfills detect missing features and provide custom implementations using existing JavaScript. For example, Array.prototype.includes() is not supported in older browsers like Internet Explorer 11:

  if (!Array.prototype.includes) {
    Array.prototype.includes = function (searchElement) {
      for (var i = 0; i < this.length; i++) {
        if (this[i] === searchElement) return true;
      }
      return false;
    };
  }

  Implementing Polyfills

  1. Identify the Missing Feature: Detect support using typeof, in, or window.
  2. Write the Fallback: Create a custom implementation.
  3. Test the Polyfill: Ensure it works across browsers.
  4. Apply the Polyfill: Use feature detection to selectively apply the polyfill.

  Considerations

  • Selective Loading: Load only for browsers that need them.
  • Feature Detection: Avoid unnecessary polyfills.
  • Size and Performance: Minimize bundle size.
  • Use Libraries: Leverage comprehensive polyfill libraries.

  Libraries and Services

  • core-js: Provides polyfills for many ECMAScript features.

    import 'core-js/actual/array/flat-map';
    [1, 2].flatMap((it) => [it, it]); // => [1, 1, 2, 2]

  • Polyfill.io: Serves polyfills based on requested features and user agents.

    <script src="https://polyfill.io/v3/polyfill.min.js"></script>

  Polyfills ensure modern JavaScript features work across all browsers, enhancing compatibility and functionality.

  5. What are server-sent events?

  Server-Sent Events (SSE) is a standard that allows servers to push updates to web clients over a single, long-lived HTTP connection. This enables real-time updates without the client constantly polling the server for new data.

  How SSE Works:

  1. Client Setup: The client creates an EventSource object, providing the URL of the server-side script that generates the event stream.
  2. Server Response: The server sets headers to indicate an event stream and starts sending events to the client.
  3. Event Format: Each event follows a specific format with fields like event, data, and id.
  4. Client Handling: The EventSource object receives events and dispatches them as browser events, which can be handled using event listeners.
  5. Reconnection: The EventSource automatically handles reconnection if the connection is lost, resuming the stream from the last received event ID.

  Key Features:

  • Unidirectional: Only the server can send data to the client.
  • Retry Mechanism: The client retries the connection if it fails.
  • Text-only Data: SSE transmits text data only.
  • Built-in Browser Support: Supported by most modern browsers.
  • Event Types: SSE supports custom event types for message categorization.
  • Last-Event-Id: The client sends the Last-Event-Id header when reconnecting, allowing the server to resume the stream.

  Implementing SSE:

  Client:

  const eventSource = new EventSource('/sse');
  eventSource.onmessage = (event) => console.log('New message:', event.data);

  Server (Node.js):

  const http = require('http');
  
  http
    .createServer((req, res) => {
      if (req.url === '/sse') {
        // Set headers for SSE
        res.writeHead(200, {
          'Content-Type': 'text/event-stream',
          'Cache-Control': 'no-cache',
          Connection: 'keep-alive',
        });
  
        // Function to send a message
        const sendMessage = (message) => {
          res.write(`data: ${message}\n\n`); // Messages are delimited with double line breaks.
        };
  
        // Send a message every 5 seconds
        const intervalId = setInterval(() => {
          sendMessage(`Current time: ${new Date().toLocaleTimeString()}`);
        }, 5000);
  
        // Handle client disconnect
        req.on('close', () => {
          clearInterval(intervalId);
          res.end();
        });
      } else {
        res.writeHead(404);
        res.end();
      }
    })
    .listen(8080, () => {
      console.log('SSE server running on port 8080');
    });

  SSE provides an efficient and straightforward way to push updates from a server to a client in real-time. It is well-suited for applications requiring continuous data streams but not full bidirectional communication.

  6. What are workers in JavaScript used for?

  JavaScript workers run scripts in background threads, offloading intensive tasks to keep the user interface responsive. There are three main types of workers in JavaScript: Web Workers / Dedicated Workers, Service Workers and Shared Workers.

  Web Workers / Dedicated Workers

  • Purpose: Handle CPU-intensive tasks (e.g., data processing, computations).
  • Communication: Use postMessage() and onmessage.
  • Security: No direct DOM access.
  • Termination: Ends when the main script unloads or explicitly terminated.

  Example: Creating a Web Worker

  main.js:

  // Check if the browser supports workers
  if (window.Worker) {
    // Create a new Worker
    const myWorker = new Worker('worker.js');
  
    // Post a message to the worker
    myWorker.postMessage('Hello, Worker!');
  
    // Listen for messages from the worker
    myWorker.onmessage = function (event) {
      console.log('Message from Worker:', event.data);
    };
  
    // Error handling
    myWorker.onerror = function (error) {
      console.error('Error from Worker:', error);
    };
  }

  worker.js:

  // Listen for messages from the main script
  onmessage = function (event) {
    console.log('Message from Main Script:', event.data);
  
    // Perform a task (e.g., some computation)
    const result = event.data + ' - Processed by Worker';
  
    // Post the result back to the main script
    postMessage(result);
  };

  Service Workers

  • Purpose: Act as a network proxy, handle requests, and cache resources.
  • Capabilities: Enable offline functionality and push notifications.
  • Lifecycle: Managed by the browser (install, activate, update).
  • Security: No direct DOM access.

  Example: Creating a Service Worker

  main.js:

  if ('serviceWorker' in navigator) {
    navigator.serviceWorker
      .register('/service-worker.js')
      .then((registration) => {
        console.log('Service Worker registered:', registration);
      })
      .catch((err) => {
        console.log('Service Worker registration failed:', err);
      });
  }

  service-worker.js:

  self.addEventListener('fetch', (event) => {
    event.respondWith(
      caches.match(event.request).then((response) => {
        return response || fetch(event.request);
      }),
    );
  });

  Shared Workers

  • Purpose: Shared across multiple scripts in different windows/tabs/iframes.
  • Use Case: State sharing across multiple browser contexts.

  Considerations and Limitations

  • Same-Origin Policy: Workers must comply with the same-origin policy.
  • No DOM Access: Communicate with the main thread via messages.
  • Performance: Managing workers incurs overhead; use judiciously.
  • Error Handling: Implement proper error handling mechanisms.

  7. What is "use strict";?** What are the advantages and disadvantages to using it?

  "use strict"; is a directive from ECMAScript 5 (ES5) that enforces stricter parsing and error handling in JavaScript, making code more secure and less error-prone.

  How to Use Strict Mode

  1. Global Scope: Add at the beginning of a JavaScript file.

     'use strict';
     function add(a, b) {
       return a + b;
     }

  2. Local Scope: Add at the beginning of a function.

     function myFunction() {
       'use strict';
       // Strict mode only within this function
     }

  Key Features of Strict Mode

  1. Error Prevention:
     • Disallows undeclared variables.
     • Prevents assignment to non-writable properties.
     • Restricts use of reserved keywords as identifiers.
  2. Improved Security:
     • Disallows deprecated features like arguments.caller.
     • Restricts eval() to prevent variable declarations in the calling scope.
  3. Compatibility:
     • Ensures future-proofing with JavaScript updates.

  Example of preventing global variables:

  javascriptCopy code
  // Without strict mode
  function defineNumber() { count = 123; }
  defineNumber();
  console.log(count); // Logs: 123
  
  // With strict mode
  'use strict';
  function strictFunc() {
    strictVar = 123; // ReferenceError
  }
  strictFunc();
  console.log(strictVar); // ReferenceError

  Is It Necessary?

  • Modules: ES6 and Node.js modules are automatically in strict mode.
  • Classes: Code within class definitions is also in strict mode.

  While "use strict"; is not mandatory in these contexts, it is still recommended for older code and broader compatibility.

  8. How can you implement secure authentication and authorization in JavaScript applications?

  To secure authentication and authorization in JavaScript applications, use HTTPS to encrypt data in transit and store sensitive data like tokens securely with localStorage or sessionStorage. Employ token-based authentication using JWTs, validating tokens server-side. Utilize libraries like OAuth for third-party authentication and enforce role-based access control (RBAC) for proper authorization.

  9. How can you optimize DOM manipulation for better performance?

  Minimize direct DOM access by batching changes, using documentFragment, and leveraging virtual DOM libraries like React. Use requestAnimationFrame for animations and avoid layout thrashing by separating DOM reads and writes.

  10. How can you optimize network requests for better performance?

  Minimize the number of requests, use caching, compress data, and leverage HTTP/2 and service workers. Combine CSS files, use Cache-Control headers for static assets, and enable Gzip compression to reduce data size.

  11. How can you prevent clickjacking attacks?

  Prevent clickjacking by using the X-Frame-Options HTTP header set to DENY or SAMEORIGIN to control iframe embedding. Additionally, use the Content-Security-Policy header with the frame-ancestors directive to specify allowed origins.

  X-Frame-Options: DENY
  Content-Security-Policy: frame-ancestors 'self'

  12. How do you validate form elements using the Constraint Validation API?

  Use the Constraint Validation API with properties like validity and validationMessage, and methods like checkValidity() and setCustomValidity(). For example:

  const input = document.querySelector('input');
  if (input.checkValidity()) {
    console.log('Input is valid');
  } else {
    console.log(input.validationMessage);
  }

  13. How does hoisting affect function declarations and expressions?

  In JavaScript, hoisting moves function declarations to the top of their scope, making them callable before their definition. Function expressions are not hoisted similarly; the variable is hoisted, but its assignment is not.

  // Function declaration
  console.log(foo()); // Works fine
  function foo() {
    return 'Hello';
  }
  
  // Function expression
  console.log(bar()); // Throws TypeError: bar is not a function
  var bar = function () {
    return 'Hello';
  };

  14. How does JavaScript garbage collection work?

  JavaScript uses automatic garbage collection to reclaim memory from objects and variables no longer in use. The two main algorithms are mark-and-sweep and generational garbage collection.

  Mark-and-Sweep

  • Marking phase: The garbage collector starts from root objects (global variables, currently executing functions) and marks all reachable objects as "in-use".
  • Sweeping phase: It then removes unmarked objects, freeing up memory.

  Generational Garbage Collection Modern engines divide objects into generations based on age and usage. Frequently accessed objects stay in younger generations, while less-used objects move to older generations, optimizing garbage collection by focusing on short-lived objects.

  Different JavaScript engines may use different garbage collection strategies.

  15. What are mocks and stubs and how are they used in testing?

  Mocks and stubs simulate real objects in testing. Stubs provide predefined responses to function calls, isolating the code being tested from external dependencies. Mocks are more complex, verifying interactions like whether a function was called and with what arguments. Stubs focus on isolating functionality, while mocks ensure correct interaction with dependencies.

  16. What are proxies in JavaScript used for?

  A proxy in JavaScript is an intermediary object that intercepts and customizes operations on another object, such as property access, assignment, and function invocation.

  Example:

  const myObject = {
    name: 'John',
    age: 42,
  };
  
  const handler = {
    get: function (target, prop) {
      console.log(`Accessed property "${prop}"`);
      return target[prop];
    },
  };
  
  const proxiedObject = new Proxy(myObject, handler);
  
  console.log(proxiedObject.name); // Logs: 'John'
  // Accessed property "name"
  
  console.log(proxiedObject.age); // Logs: 42
  // Accessed property "age"

  Use cases:

  • Property access interception: Customize behavior when properties are accessed.
  • Property assignment validation: Validate values before setting properties.
  • Logging and debugging: Log interactions with objects for debugging.
  • Creating reactive systems: Trigger updates when properties change.
  • Data transformation: Modify data being set or retrieved.
  • Mocking and stubbing in tests: Create mock objects for testing.
  • Function invocation interception: Cache and optimize frequently called methods.
  • Dynamic property creation: Define properties on-the-fly with default values.

  17. What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript?

  Using languages like TypeScript or CoffeeScript, which compile to JavaScript, has several pros and cons.

  Advantages:

  • Improved syntax and readability
  • Type safety and error checking
  • Better tooling and editor support

  Disadvantages:

  • Added build steps and complexity
  • Potential performance overhead
  • Learning curve for new syntax

  18. What are some techniques for reducing reflows and repaints?

  • Minimize DOM manipulations and batch changes.
  • Use CSS classes instead of direct style updates.
  • Simplify CSS selectors to optimize rendering.
  • Use requestAnimationFrame for synchronized animations.
  • Apply will-change to elements that change frequently.
  • Separate DOM reads and writes to avoid layout thrashing.

  19. What are some tools that can be used to measure and analyze JavaScript performance?

  Tools such as Chrome DevTools, Lighthouse, WebPageTest, and JSPerf are commonly used for this purpose. Chrome DevTools includes a Performance panel for profiling, Lighthouse provides performance audits, WebPageTest offers detailed performance testing, and JSPerf aids in comparing JavaScript snippet performance.

  20. What are Web Workers and how can they be used to improve performance?

  Web Workers enable running JavaScript in the background, independent of the main execution thread of a web application. This is beneficial for handling intensive computations without blocking the user interface. Web Workers are created using the Worker constructor and communication with them is facilitated through the postMessage and onmessage methods.

  Conclusion

  Preparing yourself to answer these questions in an interview setting will certainly help you stand out from the crowd. It's not just about knowing the answers; it's about understanding the underlying concepts and applying them effectively in real-world scenarios. Mastering these advanced JavaScript topics will not only boost your confidence during technical interviews but also equip you to build scalable and efficient web applications.

  Read more

  Open in new tab

• Advanced JavaScript Interview Questions for 10+ Years of Experience

  Explore advanced JavaScript interview questions and answers designed for engineers with 10+ years of experience, curated by big tech senior engineers.

  Level

  Advanced

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  14 min read

  Oct 26, 2024

  Copy link

  Share

  ---

  For seasoned frontend engineers with over a decade of experience, interviews delve into sophisticated topics that test problem-solving skills and architectural expertise. To help you excel in these interviews, we've curated a definitive list of 20 advanced JavaScript questions. These questions cover intricate concepts like microtask queues, closures, async/await, and more, designed to showcase your deep understanding and ability to navigate complex challenges.

  1. Explain the concept of a microtask queue?

  The microtask queue in JavaScript is where tasks like promise callbacks (then and catch), async functions, and certain APIs like MutationObserver are queued for execution. It's separate from the regular task queue and has higher priority, ensuring microtasks are processed immediately after the current execution context is clear. This queue follows FIFO (First In, First Out) order, ensuring predictable handling of asynchronous operations in JavaScript applications.

  2. What are the potential pitfalls of using closures?

  Potential pitfalls of using closures in JavaScript include:

  • Memory Leaks: Closures can unintentionally keep outer function scopes alive, causing memory leaks.
  • Variable Sharing: They can lead to unexpected variable sharing between closures.
  • Performance Issues: Overuse can impact performance due to increased memory usage.
  • Debugging Complexity: Understanding and debugging code with closures can be challenging due to the complexity of the scope chain.

  3. What is the typical use case for anonymous functions?

  Anonymous functions offer a concise way to define functions, especially for simple operations or callbacks. They are commonly used in Immediately Invoked Function Expressions (IIFEs) to encapsulate code within a local scope, preventing variables from leaking into the global scope:

  (function () {
    var x = 10;
    console.log(x); // 10
  })();
  
  // x is not accessible here
  console.log(typeof x); // undefined

  Anonymous functions are also effective as callbacks, enhancing code readability by defining handlers inline:

  setTimeout(() => {
    console.log('Hello world!');
  }, 1000);

  Moreover, they are utilized with higher-order functions like map(), filter(), and reduce() in functional programming:

  const arr = [1, 2, 3];
  const double = arr.map((el) => el * 2);
  console.log(double); // [2, 4, 6]

  In event handling, anonymous functions are widely employed in frameworks like React to define inline callback functions:

  function App() {
    return <button onClick={() => console.log('Clicked!')}>Click Me</button>;
  }

  These uses showcase how anonymous functions streamline code by keeping logic concise and scoped appropriately.

  4. What are some advantages and disadvantages of using TypeScript with JavaScript?

  Languages that compile to JavaScript, like TypeScript or CoffeeScript, offer advantages such as improved syntax, type safety, and better tooling. These languages enhance code readability, provide robust error checking, and support advanced IDE features.

  However, using such languages also introduces challenges. Developers may face additional build steps and increased complexity in their workflow. There could be potential performance overhead compared to writing directly in JavaScript. Moreover, adapting to new syntax and learning the intricacies of these languages can pose a learning curve initially.

  5. What is the Event Loop in JavaScript? How does it handle asynchronous operations?

  The event loop in JavaScript manages asynchronous operations to prevent blocking the single-threaded execution:

  Parts of the Event Loop:

  • Call Stack: Tracks and executes functions in a Last In, First Out (LIFO) manner.
  • Web APIs/Node.js APIs: Handle asynchronous tasks like setTimeout(), HTTP requests, and file I/O on separate threads.
  • Task Queue (Macrotask Queue/Callback Queue): Stores callbacks from completed asynchronous tasks.
  • Microtasks Queue: Executes higher-priority tasks immediately after the current script finishes.

  Event Loop Order:

  1. JavaScript executes synchronous code, adding tasks to the call stack.
  2. Asynchronous tasks are delegated to APIs for background processing.
  3. Completed task callbacks are queued in the task or microtasks queue.
  4. When the call stack is empty:
     • Microtasks queue is processed first.
     • Then, tasks in the macrotask queue are executed in order.

  This cycle ensures JavaScript remains responsive by handling both synchronous and asynchronous tasks efficiently.

  6. Explain the concept of data binding in JavaScript?

  Data binding in JavaScript automates the synchronization of data between the model (data source) and the view (UI). It ensures changes in one are immediately reflected in the other, enhancing application interactivity and reducing manual updates. There are two types:

  1. One-way Data Binding: Updates in the model reflect in the view.
  2. Two-way Data Binding: Changes in the model update the view and vice versa. This approach is common in frameworks like Angular, React with state management, and Vue.js, simplifying UI updates and user interactions.

  . What are the potential issues caused by hoisting?

  Hoisting in JavaScript can cause unexpected outcomes because variable and function declarations are lifted to the top of their scope during compilation. This behavior can lead to variables being accessed before their declaration, resulting in undefined values. It can also create confusion between function declarations and expressions. For instance:

  console.log(a); // undefined
  var a = 5;
  
  console.log(b); // ReferenceError: b is not defined
  let b = 10;

  In the example above, a is hoisted and initialized as undefined before it's assigned 5. However, b throws a ReferenceError because let variables aren't hoisted like var variables are.

  8. What is async/await and how does it simplify asynchronous code?

  async/await is a contemporary feature in JavaScript designed to streamline the handling of promises. When you declare a function with the async keyword, you can utilize the await keyword within that function to halt execution until a promise resolves. This approach aligns asynchronous code structure more closely with synchronous code, enhancing readability and maintainability.

  Example usage:

  async function fetchData() {
    try {
      const response = await fetch('https://api.example.com/data');
      const data = await response.json();
      console.log(data);
    } catch (error) {
      console.error('Error fetching data:', error);
    }
  }

  In this example:

  • The async function fetchData() uses await to fetch data from an API endpoint.
  • Using await ensures that each asynchronous operation completes before proceeding, simplifying error handling within the try...catch block.

  9. What are iterators and generators in JavaScript and what are they used for?

  In JavaScript, iterators and generators offer flexible ways to manage data sequences and control execution flow.

  Iterators define a sequence and terminate with a potential return value. They require a next() method that returns an object with value (next sequence value) and done (boolean indicating completion) properties.

  Example of an iterator:

  const iterator = {
    current: 0,
    last: 5,
    next() {
      if (this.current <= this.last) {
        return { value: this.current++, done: false };
      } else {
        return { value: undefined, done: true };
      }
    },
  };
  
  let result = iterator.next();
  while (!result.done) {
    console.log(result.value); // Logs 0, 1, 2, 3, 4, 5
    result = iterator.next();
  }

  Generators are special functions using function* syntax and yield keyword to control execution flow. They return an iterator object, allowing pausing and resuming execution.

  Example of a generator:

  function* numberGenerator() {
    let num = 0;
    while (num <= 5) {
      yield num++;
    }
  }
  
  const gen = numberGenerator();
  console.log(gen.next()); // { value: 0, done: false }
  console.log(gen.next()); // { value: 1, done: false }
  console.log(gen.next()); // { value: 2, done: false }
  console.log(gen.next()); // { value: 3, done: false }
  console.log(gen.next()); // { value: 4, done: false }
  console.log(gen.next()); // { value: 5, done: false }
  console.log(gen.next()); // { value: undefined, done: true }

  Generators are efficient for creating iterators on-demand, useful for lazy evaluation, custom data structures, and asynchronous data handling.

  10. What are Web Workers and how can they be used to improve performance?

  Web Workers enable JavaScript code to run in the background, separate from the main execution thread of a web application. They handle intensive computations without freezing the user interface. Here's a concise example:

  main.js:

  const worker = new Worker('worker.js');
  worker.postMessage('Hello, worker!');
  
  worker.onmessage = (event) => console.log('Message from worker:', event.data);

  worker.js:

  onmessage = (event) => {
    console.log('Message from main script:', event.data);
    postMessage('Hello, main script!');
  };

  Web Workers boost performance by offloading heavy tasks, ensuring smoother user interaction in web applications.

  11. Explain the concept of memoization in JavaScript and how it can be implemented.

  Memoization in JavaScript is a technique used to optimize functions by caching the results of expensive function calls and returning the cached result when the same inputs occur again. This can significantly improve performance by avoiding redundant calculations.

  It is particularly useful for functions that are computationally expensive but deterministic—meaning they always produce the same output for the same input.

  Example:

  Here's a concise implementation example using a Fibonacci function:

  function memoize(fn) {
    const cache = {};
    return function (...args) {
      const key = JSON.stringify(args);
      return cache[key] || (cache[key] = fn.apply(this, args));
    };
  }
  
  function fibonacci(n) {
    if (n <= 1) return n;
    return fibonacci(n - 1) + fibonacci(n - 2);
  }
  
  const memoizedFibonacci = memoize(fibonacci);
  
  console.log(memoizedFibonacci(6)); // Output: 8
  console.log(memoizedFibonacci(7)); // Output: 13
  console.log(memoizedFibonacci(6)); // Output: 8 (retrieved from cache)

  12. How can you optimize DOM manipulation for better performance?

  To optimize performance and reduce reflows and repaints, follow these strategies:

  • Minimize DOM Manipulations: Reduce direct changes to the DOM by batching updates whenever possible.
  • Batch DOM Changes: Use techniques like DocumentFragment or innerHTML to insert multiple DOM nodes at once.
  • Use CSS Classes: Apply style changes using CSS classes rather than manipulating styles directly with JavaScript.
  • Avoid Complex CSS Selectors: Simplify CSS selectors to improve rendering performance.
  • Use requestAnimationFrame: Schedule animations and layout changes using requestAnimationFrame for smoother rendering.
  • Optimize with will-change: Mark elements that will undergo frequent changes with the will-change CSS property to optimize rendering.
  • Separate Read and Write Operations: Avoid layout thrashing by reading from the DOM separately from writing to it, minimizing reflows.

  Implementing these practices helps ensure that your web application performs efficiently, maintaining smooth user interactions and responsive UI updates.

  13. What are JavaScript polyfills for?

  JavaScript polyfills are code snippets designed to replicate the behavior of modern JavaScript features on browsers that do not natively support them. They detect the absence of a specific feature and provide an alternative implementation using existing JavaScript capabilities.

  How Polyfills Operate

  For instance, consider the Array.prototype.includes() method, which verifies if an array contains a particular element. This method isn't supported in older browsers such as Internet Explorer 11. To address this gap, a polyfill for Array.prototype.includes() can be implemented as follows:

  // Polyfill for Array.prototype.includes()
  if (!Array.prototype.includes) {
    Array.prototype.includes = function (searchElement) {
      for (var i = 0; i < this.length; i++) {
        if (this[i] === searchElement) {
          return true;
        }
      }
      return false;
    };
  }

  Steps to Implement Polyfills

  1. Identify the missing feature: Determine if the feature is supported by the target browsers using methods like typeof, in, or window.
  2. Create the fallback implementation: Develop a custom solution that mimics the behavior of the missing feature using JavaScript code.
  3. Test and integrate: Thoroughly test the polyfill across various browsers to ensure consistent functionality and integrate it into your project.

  Considerations

  • Selective loading: Load polyfills only when necessary to optimize performance and minimize unnecessary code execution.
  • Feature detection: Use feature detection techniques to avoid overwriting native browser implementations and ensure seamless integration.

  Popular Polyfill Tools

  • core-js: A versatile library offering polyfills for a wide array of ECMAScript features.

  import 'core-js/actual/array/flat-map'; // Example: polyfill for Array.prototype.flatMap
  [1, 2].flatMap((it) => [it, it]); // Output: [1, 1, 2, 2]

  • Polyfill.io: A service that dynamically serves polyfills based on browser capabilities and specified feature requirements.

  <script src="https://polyfill.io/v3/polyfill.min.js"></script>

  JavaScript polyfills play a crucial role in ensuring cross-browser compatibility and enabling the adoption of modern JavaScript features in environments with varying levels of browser support.

  14. What are the benefits of using a module bundler?

  Module bundlers like Webpack, Parcel, and Rollup offer key benefits for web development:

  1. Dependency Management: Efficiently manage dependencies between JavaScript modules.
  2. Code Optimization: Bundle and optimize code for production, including minification and tree shaking.
  3. Browser Compatibility: Handle compatibility across different browsers and environments, including transpiling for older browsers.
  4. Performance: Improve performance by reducing HTTP requests and supporting caching and lazy loading.
  5. Integration: Integrate well with build tools, preprocessors, testing frameworks, and deployment workflows.

  Module bundlers streamline code organization, enhance performance, ensure compatibility, and integrate seamlessly with development tools, essential for modern web development.

  15. Explain the concept of tree shaking in module bundling?

  Tree shaking is a module bundling technique that removes dead code — code that's never used or executed — from the final bundle. This optimization reduces bundle size and enhances application performance. Tools like Webpack and Rollup support tree shaking primarily with ES6 module syntax (import/export), analyzing the code's dependency graph to eliminate unused exports efficiently.

  16. What are some common performance bottlenecks in JavaScript applications?

  Common performance bottlenecks in JavaScript applications often stem from inefficient DOM manipulation, excessive global variables, blocking the main thread with heavy computations, memory leaks, and improper use of asynchronous operations.

  To address these challenges, employing techniques such as debouncing and throttling for event handling, optimizing DOM updates with batch processing, and utilizing web workers for offloading heavy computations can significantly enhance application responsiveness and efficiency. These approaches help mitigate the impact of these bottlenecks on user experience and overall application performance.

  17. Explain the difference between unit testing, integration testing, and end-to-end testing

  Unit Testing:

  • Focus: Tests individual functions or methods in isolation.
  • Purpose: Ensures each unit of code behaves as expected.
  • Scope: Doesn't interact with external dependencies.
  • Tools: Jest, Mocha, Jasmine.

  Integration Testing:

  • Focus: Tests interactions between integrated units.
  • Purpose: Validates units work together correctly.
  • Scope: Includes databases, APIs, or external services.
  • Tools: Selenium, Postman, custom scripts.

  End-to-End Testing:

  • Focus: Tests the entire application workflow.
  • Purpose: Checks application behavior in real-world scenarios.
  • Scope: Includes UI, backend, and external dependencies.
  • Tools: Cypress, Puppeteer, Selenium WebDriver.

  Each type of testing plays a crucial role in ensuring software quality across different levels of application functionality and integration.

  18. What are some tools and techniques for identifying security vulnerabilities in JavaScript code?

  Tools:

  1. Static Analysis: ESLint with security plugins, SonarQube, CodeQL.
  2. Dynamic Analysis: OWASP ZAP, Burp Suite.
  3. Dependency Scanning: npm Audit, Snyk.
  4. Browser Tools: Chrome DevTools, Firefox Developer Tools.

  Techniques:

  1. Secure Coding Practices: Input validation, output encoding, error handling.
  2. Penetration Testing: Manual or automated tests to simulate attacks.
  3. Regular Audits: Periodic reviews to detect and fix vulnerabilities.
  4. Security Headers: Implementing headers like Content Security Policy.

  Using these tools and techniques helps ensure JavaScript applications are secure against common vulnerabilities.

  19. Explain the concept of Content Security Policy (CSP) and how it enhances security

  Content Security Policy (CSP) is a critical security feature designed to mitigate vulnerabilities like Cross-Site Scripting (XSS) and data injection attacks. By defining a whitelist of trusted sources for content such as scripts, stylesheets, and images, CSP restricts which resources a browser can load and execute on a webpage. This is typically set using HTTP headers or <meta> tags in HTML. For instance, the Content-Security-Policy header can specify that only scripts from the same origin ('self') are allowed to execute:

  content-security-policy: script-src 'self';

  This approach ensures that only trusted scripts from specified sources can run, enhancing the security of web applications by preventing unauthorized script execution and protecting against malicious code injection attempts.

  20. When would you use document.write()?

  document.write() is rarely used in modern web development because if called after the page has loaded, it can overwrite the entire document. It's typically reserved for simple tasks during initial page load, such as for educational purposes or quick debugging. Instead, it's generally recommended to use safer methods like innerHTML, appendChild(), or modern frameworks/libraries for more controlled and secure DOM manipulation.

  Conclusion

  Well done, you've reached the end! These questions serve as a comprehensive guide to showcasing your breadth and depth of knowledge in JavaScript. If you're already familiar with all of them, that's fantastic! If not, don't be disheartened; view this as an opportunity to dive deeper into these intricate topics. Mastering these concepts will not only prepare you for advanced JavaScript interviews but also strengthen your overall technical expertise.

  Read more

  Open in new tab

• JavaScript Interview Questions for 5+ Years of Experience

  Explore advanced JavaScript interview questions and answers designed for engineers with 5+ years of experience, curated by big tech senior engineers.

  Level

  Intermediate

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  16 min read

  Oct 17, 2024

  Copy link

  Share

  ---

  As a seasoned JavaScript developer with 5+ years of experience, you're likely no stranger to the intricacies of JavaScript. However, even the most experienced developers can benefit from a refresher on the most critical concepts and nuances of the language. In this article, we'll cover the top 20 JavaScript interview questions that can help you prepare effectively for your next interview.

  1. What's a typical use case for anonymous functions in JavaScript?

  Anonymous functions provide a concise way to define functions, especially useful for simple operations or callbacks. They are commonly used in:

  • Immediate execution: Encapsulate code within a local scope using Immediately Invoked Function Expressions (IIFEs).
  • Callbacks: Define handlers directly where they are called without having to search elsewhere.
  • Higher-order functions: Use as arguments to functions like map(), filter(), and reduce().
  • Event Handling: Common in React for inline event handling.

  Checkout the below code example-

  // Encapsulating Code using IIFE
  (function () {
    // Some code here.
  })();
  
  // Callbacks
  setTimeout(function () {
    console.log('Hello world!');
  }, 1000);
  
  // Functional programming constructs
  const arr = [1, 2, 3];
  const double = arr.map(function (el) {
    return el * 2;
  });
  console.log(double); // [2, 4, 6]

  2. What is a closure in JavaScript, and why would you use one?

  A closure is a function that retains access to these variables even after the outer function has finished executing. This is like the function has a memory of its original environment.

  function outerFunction() {
    const outerVar = 'I am outside of innerFunction';
  
    function innerFunction() {
      console.log(outerVar); // `innerFunction` can still access `outerVar`.
    }
  
    return innerFunction;
  }
  
  const inner = outerFunction(); // `inner` now holds a reference to `innerFunction`.
  
  inner(); // "I am outside of innerFunction"
  // Even though `outerFunction` has completed execution, `inner` still has access to variables defined inside `outerFunction`.

  Closures are useful for:

  • Data encapsulation: Create private variables and functions that can't be accessed from outside the closure.
  • Maintaining state: Particularly in functional programming and React hooks.
  • Event handlers and callbacks: Retain access to variables when handlers are defined.

  3. What are the pros and cons of using Promises instead of callbacks in JavaScript?

  Pros:

  • Avoid callback hell: Promises simplify nested callbacks.

    // Callback hell
    getData1((data) => {
      getData2(data, (data) => {
        getData3(data, (result) => {
          console.log(result);
      });
    });

  • Sequential code: Easier to write and read using .then().

  • Parallel code: Simplifies managing multiple promises with Promise.all().

    Promise.all([getData1(), getData2(), getData3()])
      .then((results) => {
        console.log(results);
      })
      .catch((error) => {
        console.error('Error:', error);
      });

  Cons:

  • Can be slightly more complex to understand initially.

  4. How do you abort a web request using AbortController in JavaScript?

  AbortController allows you to cancel ongoing asynchronous operations like fetch requests. To use it:

  1. Create an instance: const controller = new AbortController(); 2.Pass the signal: Add the signal to the fetch request options.
  2. Abort the request: Call controller.abort() to cancel the request.

  Here is an example of how to use **AbortController**s with the fetch() API:

  const controller = new AbortController();
  const signal = controller.signal;
  
  fetch('YOUR API', { signal })
    .then((response) => {
      // Handle response
    })
    .catch((error) => {
      if (error.name === 'AbortError') {
        console.log('Request aborted');
      } else {
        console.error('Error:', error);
      }
    });
  
  // Call abort() to abort the request
  controller.abort();

  Some of its use cases can be:

  • Cancel a fetch() request on a user action
  • Prioritize latest requests in a race condition
  • Cancel requests that are no longer needed

  5. Why is extending built-in JavaScript objects not a good idea?

  In JavaScript it's very easy to extend a built-in/native object. You can simply extend a built-in object by adding properties and functions to its prototype.

  String.prototype.reverseString = function () {
    return this.split('').reverse().join('');
  };
  
  console.log('hello world'.reverseString()); // Outputs 'dlrow olleh'
  
  // Instead of extending the built-in object, write a pure utility function to do it.
  
  function reverseString(str) {
    return str.split('').reverse().join('');
  }
  
  console.log(reverseString('hello world')); // Outputs 'dlrow olleh'

  While this may seem like a good idea at first, it is dangerous in practice. Imagine your code uses a few libraries that both extend the Array.prototype by adding the same contains method, the implementations will overwrite each other and your code will have unpredictable behavior if these two methods do not work the same way.

  Extending built-in objects can lead to issues such as:

  • Future-proofing: Risk of conflicts with future implementations.
  • Collisions: Potential clashes with other libraries.
  • Maintenance: Difficult for other developers to understand.
  • Performance: Potential negative impact.
  • Security: Risk of introducing vulnerabilities.
  • Compatibility: Issues across different environments.

  6. Why is it, in general, a good idea to leave the global JavaScript scope of a website as-is and never touch it?

  In the browser, the global scope refers to the top-level context where variables, functions, and objects are accessible throughout the code. This scope is represented by the window object. Variables and functions declared outside of any function or block (excluding modules) are added to the window object, making them globally accessible.

  For example:

  // This runs in the global scope, not within a module.
  let globalVar = 'Hello, world!';
  function greet() {
    console.log('Greetings from the global scope!');
  }
  
  console.log(window.globalVar); // 'Hello, world!'
  window.greet(); // 'Greetings from the global scope!'

  In this example, globalVar and greet are attached to the window object and can be accessed from anywhere in the global scope.

  Generally, it's advisable to avoid polluting the global namespace unless necessary. Key reasons include:

  • Naming conflicts: Multiple scripts sharing the global scope can lead to conflicts and bugs when new global variables or changes are introduced.
  • Cluttered global namespace: Minimizing the global namespace helps keep the codebase manageable and maintainable.
  • Scope leaks: Accidental references to global variables in closures or event handlers can result in memory leaks and performance issues.
  • Modularity and encapsulation: Good design practices involve keeping variables and functions within specific scopes, improving organization, reusability, and maintainability.
  • Security concerns: Global variables are accessible by all scripts, including potentially malicious ones, posing security risks, especially if they contain sensitive data.
  • Compatibility and portability: Relying heavily on global variables reduces code portability and complicates integration with other libraries or frameworks.

  7. Explain the differences between CommonJS modules and ES modules in JavaScript?

  In JavaScript, modules are reusable pieces of code that encapsulate functionality, making it easier to manage, maintain, and structure your applications. Modules allow you to break down your code into smaller, manageable parts, each with its own scope.

  CommonJS is an older module system that was initially designed for server-side JavaScript development with Node.js. It uses the require() function to load modules and the module.exports or exports object to define the exports of a module.

  // my-module.js
  const value = 42;
  module.exports = { value };
  
  // main.js
  const myModule = require('./my-module.js');
  console.log(myModule.value); // 42

  ES Modules (ECMAScript Modules) are the standardized module system introduced in ES6 (ECMAScript 2015). They use the import and export statements to handle module dependencies.

  // my-module.js
  export const value = 42;
  
  // main.js
  import { value } from './my-module.js';
  console.log(value); // 42

  8. Explain the difference between mutable and immutable objects in JavaScript

  Immutability is a core principle in functional programming but it has lots to offer to object-oriented programs as well.

  Mutable objects

  Mutable objects in JavaScript allow for modifications to their properties and values after creation. This behavior is default for most objects.

  let mutableObject = {
    name: 'John',
    age: 30,
  };
  
  // Modify the object
  mutableObject.name = 'Jane';
  
  console.log(mutableObject); // Output: { name: 'Jane', age: 30 }

  Mutable objects like mutableObject above can have their properties changed directly, making them flexible for dynamic updates.

  Immutable objects

  In contrast, immutable objects cannot be modified once created. Any attempt to change their content results in the creation of a new object with the updated values.

  const immutableObject = Object.freeze({
    name: 'John',
    age: 30,
  });
  
  // Attempting to modify the object
  immutableObject.name = 'Jane'; // This change won't affect the object
  
  console.log(immutableObject); // Output: { name: 'John', age: 30 }

  Here, immutableObject remains unchanged after creation due to Object.freeze(), which prevents modifications to its properties.

  The primary difference lies in modifiability. Mutable objects allow changes to their properties directly, while immutable objects ensure the integrity of their initial state by disallowing direct modifications.

  const vs immutable objects

  A common confusion is that declaring a variable using const makes the value immutable, which is not true at all.

  Using const prevents the reassignment of variables but doesn't make non-primitive values immutable.

  // Using const
  const person = { name: 'John' };
  person = { name: 'Jane' }; // Error: Assignment to constant variable
  person.name = 'Jane'; // Allowed, person.name is now 'Jane'
  
  // Using Object.freeze() to create an immutable object
  const frozenPerson = Object.freeze({ name: 'John' });
  frozenPerson.name = 'Jane'; // Fails silently (no error, but no change)
  frozenPerson = { name: 'Jane' }; // Error: Assignment to constant variable

  In the first example with const, reassigning a new object to person is not allowed, but modifying the name property is permitted. In the second example, Object.freeze() makes the frozenPerson object immutable, preventing any changes to its properties.

  9. Why might you want to create static class members in JavaScript?

  Static class members in JavaScript, denoted by the static keyword, are accessed directly on the class itself, not on instances. They serve multiple purposes:

  1. Namespace Organization: They help organize constants or configuration values within the class, preventing naming conflicts.

  class Config {
    static API_KEY = 'your-api-key';
    static FEATURE_FLAG = true;
  }
  
  console.log(Config.API_KEY); // Output: 'your-api-key'
  console.log(Config.FEATURE_FLAG); // Output: true

  2. Helper Functions: Static methods act as utility functions for the class or its instances, improving code readability.

  class Arithmetic {
    static add(a, b) {
      return a + b;
    }
    static subtract(a, b) {
      return a - b;
    }
  }
  
  console.log(Arithmetic.add(2, 3)); // Output: 5
  console.log(Arithmetic.subtract(5, 2)); // Output: 3

  3. Singleton Pattern: They can facilitate the singleton pattern, ensuring only one instance of a class exists.

  class Singleton {
    static instance;
  
    static getInstance() {
      if (!this.instance) {
        this.instance = new Singleton();
      }
      return this.instance;
    }
  }
  
  const singleton1 = Singleton.getInstance();
  const singleton2 = Singleton.getInstance();
  
  console.log(singleton1 === singleton2); // Output: true

  4. Performance Benefits: Static members reduce memory usage by being shared across all instances.

  10. What are Symbols used for in JavaScript?

  Symbols in JavaScript, introduced in ES6, are unique and immutable identifiers primarily used as object property keys to avoid name collisions. They can be created using the Symbol() function, ensuring each Symbol value is unique even if descriptions are identical. Symbol properties are non-enumerable, making them suitable for private object state.

  const sym1 = Symbol();
  const sym2 = Symbol('uniqueKey');
  
  console.log(typeof sym1); // "symbol"
  console.log(sym1 === sym2); // false, each symbol is unique
  
  const obj = {};
  const sym = Symbol('uniqueKey');
  
  obj[sym] = 'value';
  console.log(obj[sym]); // "value"

  Key characteristics include:

  • Uniqueness: Each Symbol value is unique.
  • Immutability: Symbol values cannot be changed.
  • Non-enumerability: Symbol properties are not listed in for...in loops or Object.keys().

  Global Symbols can be created using Symbol.for('key'), allowing reuse across different parts of codebases:

  const globalSym1 = Symbol.for('globalKey');
  const globalSym2 = Symbol.for('globalKey');
  
  console.log(globalSym1 === globalSym2); // true
  
  const key = Symbol.keyFor(globalSym1);
  console.log(key); // "globalKey"

  There are some well known Symbol in JavaScript like:

  • Symbol.iterator: Defines the default iterator for an object.
  • Symbol.toStringTag: Used to create a string description for an object.
  • Symbol.hasInstance: Used to determine if an object is an instance of a constructor.

  11. What are JavaScript object getters and setters for?

  JavaScript object getters and setters are essential for controlling access to object properties, offering customization when getting or setting values.

  const user = {
    _firstName: 'John',
    _lastName: 'Doe',
  
    get fullName() {
      return `${this._firstName} ${this._lastName}`;
    },
  
    set fullName(value) {
      const parts = value.split(' ');
      this._firstName = parts[0];
      this._lastName = parts[1];
    },
  };
  
  console.log(user.fullName); // Output: 'John Doe'
  user.fullName = 'Jane Smith';
  console.log(user.fullName); // Output: 'Jane Smith'

  Getters (fullName) compute values based on internal properties (_firstName and _lastName), while setters (fullName) update these properties based on assigned values ('Jane Smith'). These mechanisms enhance data encapsulation and allow for custom data handling in JavaScript objects.

  12. What tools and techniques do you use for debugging JavaScript code?

  Tools and techniques for debugging JavaScript code vary depending on the context:

  • JavaScript
    • Chrome Devtools: Provides a comprehensive set of debugging tools including breakpoints, stepping through code, watching variables, profiling performance, etc. You can learn more about it here.
    • debugger statement: Inserting debugger; in code triggers breakpoints when Devtools are open, pausing execution for inspection.
    • Traditional console.log() debugging: Using console.log() statements to output variable values and debug messages.
  • React and Redux
    • React Devtools: Facilitates debugging React component hierarchies, state, and props.**
    • Redux Devtools: Enhances debugging Redux state changes, actions, and dispatched events.
  • Vue
    • Vue Devtools: Extends Vue.js development experience with component inspection, state visualization, and event tracking.

  13. Can you give an example of a curry function and why this syntax offers an advantage?

  Currying in JavaScript is a functional programming technique where a function with multiple arguments is transformed into a sequence of nested functions, each taking a single argument. This allows for partial application of the function's arguments, meaning you can fix some arguments ahead of time and then apply the remaining arguments later.

  Here's a simple example of a curry function and why this syntax offers an advantage:

  // Example of a curry function
  function curry(fn) {
    return function curried(...args) {
      if (args.length >= fn.length) {
        return fn(...args);
      } else {
        return function (...moreArgs) {
          return curried(...args, ...moreArgs);
        };
      }
    };
  }
  
  // Example function to be curried
  function multiply(a, b, c) {
    return a * b * c;
  }
  
  // Currying the multiply function
  const curriedMultiply = curry(multiply);
  
  // Applying curried functions
  const step1 = curriedMultiply(2); // partially apply 2
  const step2 = step1(3); // partially apply 3
  const result = step2(4); // apply the final argument
  
  console.log(result); // Output: 24

  Advantages of Curry Syntax:

  • Partial Application: You can create specialized versions of functions by fixing some arguments, making it easier to reuse and compose functions.
  • Modularity and Reusability: Encourages modular programming by breaking down functions into smaller, reusable parts.
  • Flexibility: Allows for function chaining and incremental application of arguments, which can improve code readability and maintainability.

  Currying enhances the functional programming paradigm in JavaScript by enabling concise, composable, and reusable functions, promoting cleaner and more modular code.

  14. What is the difference between the document load event and the document DOMContentLoaded event?

  The DOMContentLoaded event is triggered once the initial HTML document has been fully loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading.

  In contrast, the window's load event is fired only after the DOM and all dependent resources, such as stylesheets, images, and subframes, have completely loaded.

  15. Explain how JSONP works (and how it's not really Ajax).

  JSONP (JSON with Padding) is a technique used to circumvent cross-domain restrictions in web browsers, as standard Ajax requests to different domains are generally blocked.

  Instead of using Ajax, JSONP makes a request to a cross-origin domain by dynamically creating a <script> tag with a callback query parameter, such as: https://example.com?callback=handleResponse. The server wraps the data in a function named handleResponse and returns it.

  <script>
    function handleResponse(data) {
      console.log(`User: ${data.username}`);
    }
  </script>
  
  <script src="<https://example.com?callback=handleResponse>"></script>

  For this to work, the client must define the handleResponse function in the global scope, which will be invoked when the response is received.

  JSONP poses security risks because it executes JavaScript from external sources. Therefore, it's crucial to trust the JSONP provider.

  Nowadays, CORS is the preferred method, making JSONP largely obsolete.

  16. Explain the same-origin policy with regard to JavaScript.

  The same-origin policy restricts JavaScript from making requests to different domains. An origin is specified by the combination of the URI scheme, hostname, and port number. This policy is crucial for security, as it prevents a malicious script on one page from accessing sensitive data on another page's Document Object Model (DOM). This ensures that data remains secure within its designated origin, blocking unauthorized cross-origin interactions.

  17. Explain what a single page app is and how to make one SEO-friendly.

  Single Page Apps (SPAs) are highly interactive web applications that load a single HTML page and dynamically update content as the user interacts with the app. Unlike traditional server-side rendering, SPAs use client-side rendering, fetching new data via AJAX without full-page refreshes. This approach makes the app more responsive and reduces the number of HTTP requests.

  Pros:

  • Improved responsiveness with no full-page refreshes.
  • Fewer HTTP requests, as assets are reused.
  • Clear separation between client and server, allowing independent updates.

  Cons:

  • Heavier initial load due to loading all necessary assets upfront.
  • Requires server configuration to route all requests to a single entry point.
  • SEO challenges, as some search engines may not execute JavaScript, resulting in empty content.

  To enhance SEO for SPAs, consider:

  • Server-side rendering to generate HTML on the server.
  • Using services like Prerender to render JavaScript in a browser, save static HTML, and return it to search engine crawlers.

  18. How do you organize your code?

  In the past, developers often used Backbone for models, promoting an OOP approach by creating Backbone models and attaching methods to them.

  While the module pattern remains useful, modern development often favors React/Redux, which employs a single-directional data flow based on the Flux architecture. Here, app data models are typically represented using plain objects, with utility pure functions to manipulate these objects. State changes are handled using actions and reducers, following Redux principles.

  Avoid classical inheritance when possible. If you must use it, adhere to best practices and guidelines.

  19. What is the extent of your experience with Promises and/or their polyfills?

  Possess working knowledge of it. Promises can be fulfilled, rejected, or pending, and allow users to attach callbacks for handling outcomes.

  Common polyfills include $.deferred, Q, and Bluebird. However, with ES2015 providing native support, polyfills are typically unnecessary.

  20. What's the difference between an "attribute" and a "property"?

  Attributes: Defined in HTML tags, they provide initial info for the browser (like "Hello" in <input type="text" value="Hello">).

  Properties: Belong to the DOM (JavaScript's view of the page), allowing you to access and change element info after the page loads (like updating the text field value).

  Conclusion

  You made it till the end! I hope you found these JavaScript questions helpful in preparing for your next interview. As an experienced developer, mastering both foundational and advanced concepts is key to showcasing your expertise and acing your next interview. But the most important thing to remember is that it's okay to not know everything - it's all about being willing to learn and improve.

  Read more

  Open in new tab

• JavaScript Interview Questions for 2 Years of Experience

  Explore a list of JavaScript interview questions and answers tailored for engineers with 2 years of experience, curated by big tech senior engineers.

  Level

  Intermediate

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  15 min read

  Oct 12, 2024

  Copy link

  Share

  ---

  As a JavaScript developer with 2 years of experience, you've already demonstrated your skills in building robust and scalable applications. However, the interview process can still be daunting, especially when faced with tricky technical questions. To help you prepare and showcase your expertise, we've curated a list of 30 JavaScript interview questions that are tailored to your level of experience. These questions cover advanced topics such as performance optimization, design patterns, and more, and are designed to help you demonstrate your skills and confidence in your next interviews.

  1. Explain the concept of caching and how it can be used to improve performance

  Caching involves storing copies of files or data temporarily to speed up access times. It enhances performance by minimizing the frequency of fetching data from its original source. In web development, caching techniques include utilizing browser caches, service workers, and HTTP headers such as Cache-Control to effectively implement this optimization.

  2. Explain the concept of lazy loading and how it can improve performance

  Lazy loading is a design approach that defers the loading of resources until they are required. This can notably enhance performance by decreasing initial load times and conserving bandwidth. For instance, in web development, images can be lazily loaded, ensuring they are fetched only when they enter the viewport. This is facilitated using techniques like the HTML loading="lazy" attribute or through JavaScript libraries designed for this purpose.

  <img src="image.jpg" loading="lazy" alt="Lazy loaded image" />

  3. What are design patterns and why are they useful?

  Design patterns offer reusable solutions to typical software design challenges, serving as a blueprint for solving problems across various contexts. They are beneficial as they guide developers in sidestepping common issues, enhancing code clarity, and simplifying the maintenance and scalability of applications.

  4. Explain the concept of the Prototype pattern

  The Prototype pattern is a creational pattern used to create new objects by copying an existing object, known as the prototype. This pattern is advantageous when creating a new object is more resource-intensive than cloning an existing one. In JavaScript, you can implement this pattern using methods like Object.create or by utilizing the prototype property of a constructor functions.

  const prototypeObject = {
    greet() {
      console.log('Hello, world!');
    },
  };
  
  const newObject = Object.create(prototypeObject);
  newObject.greet(); // Outputs: Hello, world!

  This pattern allows objects to inherit properties and methods from a prototype, promoting code reuse and maintaining a clear structure in object-oriented programming.

  5. Explain the concept of the Singleton pattern

  The Singleton pattern ensures that a class has only one instance and provides a global access point to that instance. It is beneficial when you need precisely one object to manage tasks or resources system-wide. In JavaScript, you can implement the Singleton pattern using closures or ES6 classes to ensure there is only one instance of a class.

  class Singleton {
    constructor() {
      if (!Singleton.instance) {
        Singleton.instance = this;
      }
      return Singleton.instance;
    }
  }
  
  const instance1 = new Singleton();
  const instance2 = new Singleton();
  
  console.log(instance1 === instance2); // true

  This pattern is useful in scenarios like managing configurations, logging, and resource sharing across an application, ensuring consistency and preventing multiple instances from being created unnecessarily.

  6. What is the Factory pattern and how is it used?

  The Factory pattern in software design enables object creation without specifying their exact class upfront. It encapsulates complex instantiation logic and is ideal for situations where object types are determined dynamically at runtime. In JavaScript, this pattern can be implemented using a factory function to create various objects based on conditions:

  function createAnimal(type) {
    if (type === 'dog') {
      return { sound: 'woof' };
    } else if (type === 'cat') {
      return { sound: 'meow' };
    }
  }
  
  const dog = createAnimal('dog');
  const cat = createAnimal('cat');

  This approach promotes code flexibility and modularity by centralizing object creation logic.

  7. Explain the Observer pattern and its use cases

  The Observer pattern is a design pattern where an object, called the subject, maintains a list of its dependents, known as observers, and notifies them of any state changes. This pattern facilitates loose coupling between objects, making it useful for implementing event-driven architectures, real-time updates in user interfaces, and data synchronization across different parts of an application. It enables components to react dynamically to changes without explicitly knowing each other, promoting flexibility and maintainability in software design.

  8. What is the Decorator pattern and how is it used?

  The Decorator pattern is a structural design pattern that allows behavior to be added to objects without affecting other instances of the same class. It wraps objects with additional functionality, extending their capabilities. For example:

  class Car {
    drive() {
      return 'Driving';
    }
  }
  
  class CarDecorator {
    constructor(car) {
      this.car = car;
    }
  
    drive() {
      return this.car.drive();
    }
  }
  
  class GPSDecorator extends CarDecorator {
    drive() {
      return `${super.drive()} with GPS`;
    }
  }
  
  const myCar = new Car();
  const myCarWithGPS = new GPSDecorator(myCar);
  console.log(myCarWithGPS.drive()); // Outputs: "Driving with GPS"

  Here, CarDecorator and GPSDecorator dynamically add features like GPS to a basic Car object, demonstrating how decorators can extend object functionalities.

  9. Explain the concept of the Strategy pattern

  The Strategy pattern is a behavioral design pattern that allows you to encapsulate different algorithms into separate classes that are interchangeable. It enables the selection of algorithms at runtime without modifying client code. Here’s a concise example:

  class Context {
    constructor(strategy) {
      this.strategy = strategy;
    }
  
    execute(data) {
      return this.strategy.algorithm(data);
    }
  }
  
  class ConcreteStrategyA {
    algorithm(data) {
      // Implementation of algorithm A
      return data.sort(); // Example: sorting algorithm
    }
  }
  
  class ConcreteStrategyB {
    algorithm(data) {
      // Implementation of algorithm B
      return data.reverse(); // Example: reverse algorithm
    }
  }
  
  // Usage
  const context = new Context(new ConcreteStrategyA());
  const data = [3, 1, 2];
  console.log(context.execute(data)); // Outputs: [1, 2, 3]
  
  context.strategy = new ConcreteStrategyB();
  console.log(context.execute(data)); // Outputs: [3, 2, 1]

  In this pattern, Context manages the selected strategy object, which performs its specific algorithm on data. This approach allows flexible algorithm switching and enhances code maintainability by separating algorithms from client code.

  10. What is the Command pattern and how is it used?

  The Command pattern is a behavioral design pattern that turns a request into a stand-alone object containing all information about the request. This transformation allows for parameterization of methods with different requests, queuing of requests, and logging of the requests. It also supports undoable operations. In JavaScript, it can be implemented by creating command objects with execute and undo methods.

  class Command {
    execute() {}
    undo() {}
  }
  
  class LightOnCommand extends Command {
    constructor(light) {
      super();
      this.light = light;
    }
    execute() {
      this.light.on();
    }
    undo() {
      this.light.off();
    }
  }
  
  class Light {
    on() {
      console.log('Light is on');
    }
    off() {
      console.log('Light is off');
    }
  }
  
  const light = new Light();
  const lightOnCommand = new LightOnCommand(light);
  lightOnCommand.execute(); // Light is on
  lightOnCommand.undo(); // Light is off

  11. What is the Module pattern and how does it help with encapsulation?

  The Module pattern in JavaScript is a design pattern used to create self-contained modules of code. It helps with encapsulation by allowing you to define private and public members within a module. Private members are not accessible from outside the module, while public members are exposed through a returned object. This pattern helps in organizing code, avoiding global namespace pollution, and maintaining a clean separation of concerns.

  var myModule = (function () {
    var privateVar = 'I am private';
  
    function privateMethod() {
      console.log(privateVar);
    }
  
    return {
      publicMethod: function () {
        privateMethod();
      },
    };
  })();
  
  myModule.publicMethod(); // Logs: I am private

  12. How can you avoid problems related to hoisting?

  To avoid issues related to hoisting in JavaScript, use let or const to declare variables instead of var. Unlike var, let and const are block-scoped, meaning they are only accessible within the block they are defined in and are not hoisted to the top of the scope. Additionally, ensure functions are declared before they are called to prevent any unexpected behavior due to function hoisting.

  // Use let or const
  let x = 10;
  const y = 20;
  
  // Declare functions before calling them
  function myFunction() {
    console.log('Hello, world!');
  }
  myFunction();

  13. How can you share code between JavaScript files?

  To share code between JavaScript files, you can use modules. In modern JavaScript, ES6 modules with export and import statements are commonly used. Here's how you can export a function from one file and import it into another:

  Using ES6 Modules:

  // file1.js
  export function greet() {
    console.log('Hello, world!');
  }
  
  // file2.js
  import { greet } from './file1.js';
  greet();

  Alternatively, in Node.js, you can use module.exports and require:

  Using CommonJS Modules (Node.js):

  // file1.js
  module.exports = function greet() {
    console.log('Hello, world!');
  };
  
  // file2.js
  const greet = require('./file1.js');
  greet();

  14. How do you get the query string values of the current page in JavaScript?

  To retrieve query string values from the current page's URL in JavaScript using URLSearchParams, you can follow these steps:

  // Assuming the URL is: http://example.com/page?key=value&foo=bar
  
  // Create a URLSearchParams object from the current page's query string
  const params = new URLSearchParams(window.location.search);
  
  // Retrieve specific query parameter values
  const keyValue = params.get('key'); // 'value'
  const fooValue = params.get('foo'); // 'bar'
  
  // Example usage
  console.log(keyValue); // Outputs: 'value'
  console.log(fooValue); // Outputs: 'bar'

  This approach allows you to easily access and manipulate query string parameters directly from the browser's URL.

  15. How do you handle errors in asynchronous operations?

  Handling errors in asynchronous operations can be done effectively with both async/await and Promises:

  Using async/await with try...catch:

  javascriptCopy code
  async function fetchData() {
    try {
      const response = await fetch('https://api.example.com/data');
      if (!response.ok) throw new Error('Failed to fetch data');
      const data = await response.json();
      console.log(data);
    } catch (error) {
      console.error('Error fetching data:', error.message);
    }
  }

  Using Promises with .catch() method:

  javascriptCopy code
  fetch('https://api.example.com/data')
    .then(response => {
      if (!response.ok) throw new Error('Failed to fetch data');
      return response.json();
    })
    .then(data => console.log(data))
    .catch(error => console.error('Error fetching data:', error.message));

  These methods ensure that errors, such as network failures or failed requests, are caught and handled appropriately, maintaining robust error management in your JavaScript applications.

  16. How do you manipulate CSS styles using JavaScript?

  You can manipulate CSS styles in JavaScript by directly accessing an element's style property for specific changes like background color or font size:

  // Changing background color
  document.getElementById('myDiv').style.backgroundColor = 'blue';

  You can also add, remove, or toggle CSS classes using the classList property:

  document.getElementById('myDiv').classList.add('newClass');
  document.getElementById('myDiv').classList.remove('oldClass');
  document.getElementById('myDiv').classList.toggle('toggleClass');

  17. What are the common pitfalls of using the this keyword?

  Using the this keyword can be tricky because its value depends on the function's invocation context. Common pitfalls include losing this context when passing methods as callbacks, using this inside nested functions, and misunderstanding this in arrow functions. To address these issues, developers often use methods like .bind(), arrow functions, or store this context in a variable.

  18. What is the DOM and how is it structured?

  The DOM, or Document Object Model, is a programming interface for web documents. It represents the page so that programs can change the document structure, style, and content. The DOM is structured as a tree of objects, where each node represents part of the document, such as elements, attributes, and text nodes.

  19. What do you think of AMD vs CommonJS?

  AMD (Asynchronous Module Definition) and CommonJS are JavaScript module systems. AMD focuses on asynchronous loading, ideal for browsers, using define() and require(). CommonJS, geared towards server-side environments like Node.js, employs module.exports and require() for synchronous module loading.

  20. What are the different ways to make an API call in JavaScript?

  In JavaScript, there are several methods to make API calls. The traditional way is using XMLHttpRequest, which is more verbose. fetch is a modern approach that returns promises, making it easier to handle responses. Alternatively, Axios is a widely-used third-party library that simplifies API calls and offers additional features.

  21. What are some tools that can be used for JavaScript testing?

  For JavaScript testing, tools like Jest, Mocha, Jasmine, and Cypress are commonly used. Jest is praised for its simplicity and built-in functionalities. Mocha offers flexibility and can be integrated with various libraries. Jasmine is known for its straightforward setup and behavior-driven development (BDD) approach. Cypress excels in end-to-end testing, emphasizing real browser interactions.

  22. What is the difference between event.preventDefault() and event.stopPropagation()?

  event.preventDefault() prevents the default action of an event, like stopping a form submission whereas event.stopPropagation() prevents the event from bubbling up to parent elements.

  23. What is the difference between innerHTML and textContent?

  innerHTML returns or sets the HTML markup inside an element, allowing HTML tags to be parsed and rendered whereas textContent retrieves or sets the text content inside an element, rendering HTML tags as plain text.

  // Example of innerHTML
  element.innerHTML = '<strong>Bold Text</strong>'; // Renders as bold text
  
  // Example of textContent
  element.textContent = '<strong>Bold Text</strong>'; // Renders as plain text: <strong>Bold Text</strong>

  24. What is the difference between the window object and the document object?

  The window object represents the browser window, offering methods to control it (e.g., opening new windows, or accessing browser history). The document object represents the web page's content within the window, providing methods to manipulate the DOM (e.g., selecting elements, and modifying content).

  25. What is the difference between setTimeout(), setImmediate(), and process.nextTick()?

  setTimeout() schedules a callback to run after a minimum delay. setImmediate() schedules a callback to run after the current event loop completes. process.nextTick() schedules a callback to run before the next event loop iteration begins.

  setTimeout(() => console.log('setTimeout'), 0);
  setImmediate(() => console.log('setImmediate'));
  process.nextTick(() => console.log('nextTick'));

  In this example, process.nextTick() executes first, followed by either setTimeout() or setImmediate() depending on the environment.

  26. How do you use window.history API?

  The window.history API allows you to manipulate the browser's session history. You can use history.pushState() to add a new entry to the history stack, history.replaceState() to modify the current entry, and history.back(), history.forward(), and history.go() to navigate through the history.

  // Add a new entry to the history
  history.pushState({ page: 1 }, 'title 1', '?page=1');
  
  // Replace the current history entry
  history.replaceState({ page: 2 }, 'title 2', '?page=2');
  
  // Navigate back, forward, or to a specific point in history
  history.back(); // Go back one step
  history.forward(); // Go forward one step
  history.go(-2); // Go back two steps

  27. What are the pros and cons of using Promises instead of callbacks in JavaScript?

  Pros of Promises over Callbacks:

  • Avoids Callback Hell: Promises provide a more linear and readable structure compared to deeply nested callbacks.
  • Sequential Execution: Easily write sequential asynchronous code using .then(), improving readability and maintainability.
  • Parallel Execution: Use Promise.all() for parallel asynchronous operations, handling multiple promises concisely.

  Cons:

  • Slightly More Complex: Some developers find promises marginally more complex compared to straightforward callbacks.

  28. What are the metadata fields of a module?

  Metadata fields of a module often include the module's name, version, description, author, license, and dependencies. These fields are commonly found in a package.json file in JavaScript projects.

  Example:

  {
    "name": "my-module",
    "version": "1.0.0",
    "description": "A sample module",
    "author": "John Doe",
    "license": "MIT",
    "dependencies": {
      "express": "^4.17.1"
    }
  }

  These fields provide essential information about the module and its requirements.

  29. What are the different types of errors in JavaScript?

  In JavaScript, there are three main types of errors:

  1. Syntax Errors: Occur when the code violates the language's grammar rules, like missing a parenthesis.
  2. Runtime Errors: Happen during code execution, such as trying to access a property of undefined.
  3. Logical Errors: Mistakes in the code's logic that lead to incorrect results without throwing an error.

  30. Explain the concept of error propagation in JavaScript

  Error propagation in JavaScript refers to the process of passing errors up the call stack. When an error occurs in a function, it can be caught and handled with try...catch blocks. If not caught, the error moves up the call stack until it is either caught or causes the program to terminate. For example:

  function a() {
    throw new Error('An error occurred');
  }
  
  function b() {
    a();
  }
  
  try {
    b();
  } catch (e) {
    console.error(e.message); // Outputs: An error occurred
  }

  In this example, the error thrown in function a propagates to function b and is caught in the try...catch block.

  Conclusion

  You've reached the end of our list of 30 JavaScript interview questions! We hope these questions have helped you identify areas for improvement and solidify your understanding of advanced JavaScript concepts. Remember, the key to acing an interview is not just about knowing the answers, but also about demonstrating your thought process, problem-solving skills, and ability to communicate complex ideas simply.

  Read more

  Open in new tab

• Basic JavaScript Interview Questions and Answers For Freshers

  Brush up on fundamental JavaScript skills with these essential interview questions and answers. Perfect for freshers preparing for junior developer roles.

  Level

  Starter

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  44 min read

  Oct 5, 2024

  Copy link

  Share

  ---

  JavaScript is a fundamental skill for any aspiring web developer, and landing a job in this field can be a challenging task, especially for freshers. One of the most crucial steps in the interview process is the technical interview, where your JavaScript skills are put to the test. To help you prepare and boost your confidence, we've compiled a list of the top 50 basic JavaScript interview questions and answers that are commonly asked in interviews.

  1. Explain the concept of "hoisting" in JavaScript

  Hoisting describes the behavior of variable declarations in JavaScript. Declarations using var are "moved" to the top of their scope during compilation. Only the declaration is hoisted, not the initialization.

  Example with var:

  console.log(foo); // undefined
  var foo = 1;
  console.log(foo); // 1

  Visualized as:

  var foo;
  console.log(foo); // undefined
  foo = 1;
  console.log(foo); // 1

  Variables with let, const, and class:

  These are also hoisted but not initialized. Accessing them before declaration results in a ReferenceError.

  console.log(y); // ReferenceError: Cannot access 'y' before initialization
  let y = 'local';
  
  console.log(z); // ReferenceError: Cannot access 'z' before initialization
  const z = 'local';
  
  console.log(Foo); // ReferenceError: Cannot access 'Foo' before initialization
  class Foo {
    constructor() {}
  }

  Function Expressions:

  Only the declaration is hoisted.

  console.log(bar); // undefined
  bar(); // Uncaught TypeError: bar is not a function
  
  var bar = function () {
    console.log('BARRRR');
  };

  Function Declarations:

  Both declaration and definition are hoisted.

  console.log(foo); // [Function: foo]
  foo(); // 'FOOOOO'
  
  function foo() {
    console.log('FOOOOO');
  }

  Import Statements:

  Imports are hoisted, making them available throughout the module, with side effects occurring before other code runs.

  foo.doSomething(); // Works normally.
  import foo from './modules/foo';

  2. What are the differences between JavaScript variables created using let, var or const?

  Scope

  • var: Function-scoped or globally scoped.
  • let and const: Block-scoped (only accessible within the nearest set of curly braces).

  Example:

  function foo() {
    var bar = 1;
    let baz = 2;
    const qux = 3;
  
    console.log(bar); // 1
    console.log(baz); // 2
    console.log(qux); // 3
  }
  
  console.log(bar); // ReferenceError
  console.log(baz); // ReferenceError
  console.log(qux); // ReferenceError

  if (true) {
    var bar = 1;
    let baz = 2;
    const qux = 3;
  }
  
  console.log(bar); // 1
  console.log(baz); // ReferenceError
  console.log(qux); // ReferenceError

  Initialization

  • var and let: Can be declared without an initial value.
  • const: Must be initialized at the time of declaration.

  Example:

  var foo; // Ok
  let bar; // Ok
  const baz; // SyntaxError

  Redeclaration

  • var: Allows redeclaration.
  • let and const: Do not allow redeclaration.

  Example:

  var foo = 1;
  var foo = 2; // Ok
  
  let baz = 3;
  let baz = 4; // SyntaxError

  Reassignment

  • var and let: Allow reassignment.
  • const: Does not allow reassignment.

  Example:

  var foo = 1;
  foo = 2; // Ok
  
  let bar = 3;
  bar = 4; // Ok
  
  const baz = 5;
  baz = 6; // TypeError

  Accessing before declaration

  • var: Variables are hoisted and initialized to undefined.
  • let and const: Variables are hoisted but not initialized, causing a ReferenceError if accessed before declaration.

  Example:

  console.log(foo); // undefined
  var foo = 'foo';
  
  console.log(baz); // ReferenceError
  let baz = 'baz';
  
  console.log(bar); // ReferenceError
  const bar = 'bar';

  3. What is the difference between == and === in JavaScript?

  Equality Operator (==)

  • Performs type coercion, converting values to a common type before comparison.
  • Can yield unintuitive results due to type conversion.

  Examples:

  42 == '42'; // true
  0 == false; // true
  null == undefined; // true
  [] == false; // true
  '' == false; // true

  ###Strict Equality Operator (===)

  • Does not perform type coercion.
  • Both value and type must be the same for the comparison to return true.

  Examples:

  42 === '42'; // false
  0 === false; // false
  null === undefined; // false
  [] === false; // false
  '' === false; // false

  Best Practices

  • Use == only when comparing against null or undefined for convenience.

    var a = null;
    console.log(a == null); // true
    console.log(a == undefined); // true

  • Prefer === for all other comparisons to avoid pitfalls of type coercion and ensure both value and type are the same.

  4. What is the event loop in JavaScript?

  The event loop is crucial for handling asynchronous operations in JavaScript, allowing single-threaded execution without blocking.

  Components

  1. Call Stack:

  • Tracks function execution in LIFO order.
  • Functions are added and removed as they are called and complete.

  2. Web APIs/Node.js APIs:

  • Handle asynchronous tasks (setTimeout(), HTTP requests) on separate threads.

  3. Task Queue (Macrotask Queue):

  • Holds tasks like setTimeout(), setInterval(), and UI events.

  4. Microtask Queue:

  • Contains high-priority tasks (e.g., Promise callbacks).
  • Executes after the current script but before the next macrotask.

  Execution Order

  1. Script Execution:
     • Synchronous tasks are placed on the call stack.
  2. Asynchronous Operations:
     • Offloaded to Web APIs/Node.js APIs.
  3. Task Completion:
     • Completed tasks are queued in the appropriate task or microtask queue.
  4. Event Loop Monitoring:
     • Executes tasks from the call stack.
     • When the stack is empty:
       • Processes the microtask queue until empty.
       • Processes one macrotask, then checks the microtask queue again.
       • Repeats indefinitely.

  Example

  console.log('Start');
  
  setTimeout(() => {
    console.log('Timeout 1');
  }, 0);
  
  Promise.resolve().then(() => {
    console.log('Promise 1');
  });
  
  setTimeout(() => {
    console.log('Timeout 2');
  }, 0);
  
  console.log('End');

  Console Output:

  Start
  End
  Promise 1
  Timeout 1
  Timeout 2

  Explanation:

  • Start and End are logged first (synchronous).
  • Promise 1 is logged next (microtask).
  • Timeout 1 and Timeout 2 are logged last (macrotasks).

  Understanding the event loop helps write efficient, non-blocking JavaScript code.

  5. Explain event delegation in JavaScript

  Event delegation is an efficient way to handle events on multiple child elements by attaching a single event listener to a common parent element. This is useful for managing events on many similar elements, like list items.

  How Event Delegation Works

  1. Attach Listener to Ancestor:
     • Attach one listener to a parent element instead of individual listeners on each child.
  2. Event Bubbling:
     • When an event occurs on a child, it bubbles up to the parent, where the listener can handle it.
  3. Determine the Target:
     • Use event.target to identify the actual element that triggered the event.
  4. Perform Action:
     • Execute actions based on the target element.

  Benefits of Event Delegation

  • Efficiency: Fewer event listeners improve memory and performance.
  • Dynamic Elements: Automatically handles new or removed child elements.

  Example

  // HTML:
  // <ul id="item-list">
  //   <li>Item 1</li>
  //   <li>Item 2</li>
  //   <li>Item 3</li>
  // </ul>
  
  const itemList = document.getElementById('item-list');
  
  itemList.addEventListener('click', (event) => {
    if (event.target.tagName === 'LI') {
      console.log(`Clicked on ${event.target.textContent}`);
    }
  });

  A single click listener on <ul> handles clicks on any <li> due to event bubbling.

  Use Cases

  1. Dynamic Content:

     const buttonContainer = document.getElementById('button-container');
     const addButton = document.getElementById('add-button');
     
     buttonContainer.addEventListener('click', (event) => {
       if (event.target.tagName === 'BUTTON') {
         console.log(`Clicked on ${event.target.textContent}`);
       }
     });
     
     addButton.addEventListener('click', () => {
       const newButton = document.createElement('button');
       newButton.textContent = `Button ${buttonContainer.children.length + 1}`;
       buttonContainer.appendChild(newButton);
     });

  2. Simplifying Code:

     const userForm = document.getElementById('user-form');
     
     userForm.addEventListener('input', (event) => {
       const { name, value } = event.target;
       console.log(`Changed ${name}: ${value}`);
     });

  6. Explain how this works in JavaScript

  The this keyword in JavaScript can be quite confusing as its value depends on how a function is called. Here are the main rules that determine the value of this:

  1. Using the new Keyword

  Creates a new object and sets this to that object.

  function Person(name) {
    this.name = name;
  }
  const person = new Person('Alice');
  console.log(person.name); // 'Alice

  2. Using apply, call, or bind

  Explicitly sets this to a specified object.

  javascriptCopy code
  function greet() {
    console.log(this.name);
  }
  const person = { name: 'Alice' };
  greet.call(person); // 'Alice'

  3. Method Call

  this is bound to the object the method is called on.

  const obj = {
    name: 'Alice',
    greet: function () {
      console.log(this.name);
    },
  };
  obj.greet(); // 'Alice'

  4. Free Function Invocation

  In non-strict mode, defaults to the global object (window in browsers); in strict mode, defaults to undefined.

  function greet() {
    console.log(this); // global object or undefined
  }
  greet();

  5. Arrow Functions (ES6):

  Inherit this from their lexical enclosing scope.

  const obj = {
    name: 'Alice',
    greet: () => {
      console.log(this.name); // `this` refers to the enclosing scope
    },
  };
  obj.greet(); // undefined

  ES2015 (ES6) and this

  ES2015 introduced arrow functions which capture this from their lexical scope. This can simplify code but requires caution when integrating with libraries expecting traditional function context.

  Example:

  function Timer() {
    this.seconds = 0;
    setInterval(() => {
      this.seconds++; // `this` refers to the Timer instance
      console.log(this.seconds);
    }, 1000);
  }
  
  const timer = new Timer();

  7. Describe the difference between a cookie, sessionStorage and localStorage.

  Cookies, localStorage, and sessionStorage are key client-side storage mechanisms in web applications, each serving distinct purposes:

  Cookies

  • Purpose: Stores small data pieces sent to the server with HTTP requests.

  • Capacity: Limited to around 4KB per domain.

  • Lifespan: Can have expiration dates; session cookies are cleared when the browser closes.

  • Access: Domain-specific; accessible across pages and subdomains.

  • Security: Supports HttpOnly and Secure flags to restrict JavaScript access and ensure HTTPS transmission.

  • Example Usage:

    // Set a cookie with an expiry
    document.cookie =
      'auth_token=abc123def; expires=Fri, 31 Dec 2024 23:59:59 GMT; path=/';
    
    // Read all cookies (no direct method for specific cookies)
    console.log(document.cookie);
    
    // Delete a cookie
    document.cookie =
      'auth_token=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/';

  localStorage

  • Purpose: Stores data persistently on the client-side.

  • Capacity: Around 5MB per origin.

  • Lifespan: Data remains until explicitly cleared.

  • Access: Available across all tabs and windows within the same origin.

  • Security: All JavaScript on the page can access localStorage values.

  • Example Usage:

    // Set an item in localStorage
    localStorage.setItem('key', 'value');
    
    // Get an item from localStorage
    console.log(localStorage.getItem('key'));
    
    // Remove an item from localStorage
    localStorage.removeItem('key');
    
    // Clear all data in localStorage
    localStorage.clear();

  sessionStorage

  • Purpose: Stores session-specific data that persists until the browser or tab is closed.

  • Capacity: Similar to localStorage, around 5MB per origin.

  • Lifespan: Cleared when the tab or browser closes; reloading the page retains data.

  • Access: Limited to the current tab or window.

  • Security: All JavaScript on the page can access sessionStorage values.

  • Example Usage:

    // Set an item in sessionStorage
    sessionStorage.setItem('key', 'value');
    
    // Get an item from sessionStorage
    console.log(sessionStorage.getItem('key'));
    
    // Remove an item from sessionStorage
    sessionStorage.removeItem('key');
    
    // Clear all data in sessionStorage
    sessionStorage.clear();

  8. Describe the difference between <script>, <script async> and <script defer>

  <script> Tag

  The <script> tag is used to include JavaScript in a web page. When used without async or defer attributes:

  • Behavior: HTML parsing halts while the script is fetched and executed immediately.
  • Usage: Suitable for critical scripts required for initial page rendering.

  Example:

  <!doctype html>
  <html>
    <head>
      <title>Regular Script</title>
    </head>
    <body>
      <h1>Regular Script Example</h1>
      <p>This content appears before the script executes.</p>
  
      <script src="regular.js"></script>
  
      <p>This content appears after the script executes.</p>
    </body>
  </html>

  <script async> Tag

  • Behavior: Downloads the script asynchronously while HTML parsing continues. Executes the script as soon as it's available, potentially before HTML parsing completes.
  • Usage: Suitable for independent scripts like analytics or ads.

  Example:

  <!doctype html>
  <html>
    <head>
      <title>Async Script</title>
    </head>
    <body>
      <h1>Async Script Example</h1>
      <p>This content appears before the async script executes.</p>
  
      <script async src="async.js"></script>
  
      <p>This content may appear before or after the async script executes.</p>
    </body>
  </html>

  <script defer> Tag:

  • Behavior: Downloads the script asynchronously while HTML parsing proceeds. Executes the script after the HTML document is fully parsed but before DOMContentLoaded.
  • Usage: Ideal for scripts dependent on a fully-parsed DOM structure.

  Example:

  <!doctype html>
  <html>
    <head>
      <title>Deferred Script</title>
    </head>
    <body>
      <h1>Deferred Script Example</h1>
      <p>This content appears before the deferred script executes.</p>
  
      <script defer src="deferred.js"></script>
  
      <p>This content appears before the deferred script executes.</p>
    </body>
  </html>

  9. What's the difference between a variable that is: null, undefined or undeclared?

  Undeclared: A variable that is not declared using var, let, or const will be created globally and can cause errors. Avoid them by using try/catch blocks to detect them.

  undefined: A declared variable without an assigned value is undefined. Use === or typeof to check for undefined. Note that == will also return true for null.

  null: A variable explicitly assigned null represents no value. Use === to check for null. Don't use == as it will also return true for undefined.

  Best Practices:

  • Always declare variables before using them.
  • Assign null to variables if you don't intend to use them yet.
  • Use static analysis tools like ESLint or TypeScript Compiler to detect undeclared variables.

  10. What's the difference between .call and .apply in JavaScript?

  .call and .appl are used to invoke functions, setting this within the function. The difference lies in how they handle arguments:

  • .call: Takes comma-separated arguments.
  • .apply: Takes an array of arguments.

  Memory Aid:

  • C for call and comma-separated.
  • A for apply and array.

  Example:

  javascriptCopy code
  function add(a, b) {
    return a + b;
  }
  
  console.log(add.call(null, 1, 2)); // 3
  console.log(add.apply(null, [1, 2])); // 3
  
  // ES6 with spread operator
  console.log(add.call(null, ...[1, 2])); // 3

  11. Explain Function.prototype.bind

  Function.prototype.bind creates a new function with a specific this context and optionally preset arguments. It's useful for maintaining the correct this value in methods passed to other functions.

  Example:

  const john = {
    age: 42,
    getAge: function () {
      return this.age;
    },
  };
  
  console.log(john.getAge()); // 42
  
  const unboundGetAge = john.getAge;
  console.log(unboundGetAge()); // undefined
  
  const boundGetAge = john.getAge.bind(john);
  console.log(boundGetAge()); // 42
  
  const mary = { age: 21 };
  const boundGetAgeMary = john.getAge.bind(mary);
  console.log(boundGetAgeMary()); // 21

  Its main purposes are:

  1. Binding this to preserve context: The primary function of bind is to attach the this value of a function to a specific object. When you use func.bind(thisArg), it generates a new function with the same code as func, but with this permanently set to thisArg.
  2. Partial application of arguments: bind also enables you to pre-set arguments for the new function. Any arguments provided to bind after thisArg will be prepended to the argument list when the new function is invoked.
  3. Method borrowing: bind allows you to borrow methods from one object and use them on another object, even if the methods were not initially designed for that object.

  12. What advantage is there for using the arrow syntax for a method in a constructor?

  The advantage of using the arrow syntax for a method in a constructor is that it automatically binds the this value to the constructor's this context. This means that when the method is called, it will always refer to the constructor's this context, rather than the global scope or some other unexpected context.

  In traditional function expressions, the this value is determined by how the function is called, which can lead to unexpected behavior if not properly bound. By using an arrow function, you can ensure that the this value is always bound to the constructor's this context, making your code more predictable and easier to maintain.

  For example, in the code snippet:

  const Person = function (name) {
    this.name = name;
    this.sayName1 = function () {
      console.log(this.name);
    };
    this.sayName2 = () => {
      console.log(this.name);
    };
  };
  const john = new Person('John');
  const dave = new Person('Dave');
  
  john.sayName1(); // John
  john.sayName2(); // John
  
  // `this` can change for regular functions but not for arrow functions
  john.sayName1.call(dave); // Dave
  john.sayName2.call(dave); // John

  The sayName1 method uses a traditional function expression, which means its this value is determined by how it's called. If you call john.sayName1.call(dave), the this value will be dave, and the method will log Dave to the console.

  On the other hand, the sayName2 method uses an arrow function, which means its this value is automatically bound to the constructor's this context. If you call john.sayName2.call(dave), the this value will still be john, and the method will log John to the console.

  This can be particularly helpful in React class components, where you often need to pass methods as props to child components. By using arrow functions, you can ensure that the methods always refer to the correct this context, without having to manually bind this in the constructor.

  13. Explain how prototypal inheritance works

  Prototypical inheritance allows objects to inherit properties and methods from other objects using a prototype-based model.

  Key Concepts

  1. Prototypes

  • Every object has a prototype, another object it inherits from.
  • Access or modify prototypes using Object.getPrototypeOf() and Object.setPrototypeOf().

  function Person(name, age) {
    this.name = name;
    this.age = age;
  }
  
  Person.prototype.sayHello = function () {
    console.log(
      `Hello, my name is ${this.name} and I am ${this.age} years old.`,
    );
  };
  
  let john = new Person('John', 30);
  john.sayHello(); // "Hello, my name is John and I am 30 years old."

  2. Prototype Chain

  JavaScript looks for properties/methods on the object, then its prototype, and so on up the chain until null.

  3. Constructor Functions

  Functions used with new to create objects, setting their prototype to the constructor's prototype.

  function Animal(name) {
    this.name = name;
  }
  
  Animal.prototype.sayName = function () {
    console.log(`My name is ${this.name}`);
  };
  
  function Dog(name, breed) {
    Animal.call(this, name);
    this.breed = breed;
  }
  
  Dog.prototype = Object.create(Animal.prototype);
  Dog.prototype.bark = function () {
    console.log('Woof!');
  };
  
  let fido = new Dog('Fido', 'Labrador');
  fido.bark(); // "Woof!"
  fido.sayName(); // "My name is Fido"

  4. Object.create()

  Creates a new object with a specified prototype.

  let proto = {
    greet: function () {
      console.log(`Hello, my name is ${this.name}`);
    },
  };
  
  let person = Object.create(proto);
  person.name = 'John';
  person.greet(); // "Hello, my name is John"

  14. Difference between: function Person(){}, const person = Person(), and const person = new Person()?

  Function Declaration

  function Person(){} is a standard function declaration in JavaScript. When written in PascalCase, it follows the convention for functions intended to be used as constructors.

  Function Call

  const person = Person() simply calls the function and executes its code. If no return value is specified, person will be undefined. This is not a constructor call and does not create a new object.

  Constructor Call

  const person = new Person() creates a new object using the Person constructor function. The new keyword creates a new object and sets its prototype to Person.prototype. The this keyword inside the constructor function refers to the new object being created.

  15. Explain the differences on the usage of foo between function foo() {} and var foo = function() {}

  Function Declarations

  • Syntax: function foo() {}

  • Description: Defines a named function that can be called throughout the enclosing scope.

  • Example:

    function foo() {
      console.log('FOOOOO');
    }

  Function Expressions

  • Syntax: var foo = function() {}

  • Description: Defines a function and assigns it to a variable, often used in specific contexts.

  • Example:

    var foo = function () {
      console.log('FOOOOO');
    };

  Key Differences

  Hoisting:

  • Function Declarations: The entire function is hoisted; can be called before its definition.

    foo(); // 'FOOOOO'
    function foo() {
      console.log('FOOOOO');
    }

  • Function Expressions: Only the variable is hoisted, not the function body; calling it before definition results in an error.

    foo(); // Uncaught TypeError: foo is not a function
    var foo = function () {
      console.log('FOOOOO');
    };

  Name Scope:

  • Function Expressions: These can be named internally, but the name is only accessible within the function.

    const myFunc = function namedFunc() {
      console.log(namedFunc); // Works
    };
    console.log(namedFunc); // undefined

  Usage Recommendations

  Function Declarations:

  • Use for reusable functions available throughout the scope.

  Function Expressions:

  • Use for functions needed only in specific contexts to limit the scope.

  16. What are the various ways to create objects in JavaScript?

  Here are the various ways to create objects in JavaScript:

  1. Object Literals ({}): Simplest way to create objects using key-value pairs within curly braces.

     const person = {
       firstName: 'John',
       lastName: 'Doe',
     };

  2. Object() Constructor: Using the new keyword with the built-in Object constructor to create an object.

     const person = new Object();
     person.firstName = 'John';
     person.lastName = 'Doe';

  3. Object.create() Method: Creating a new object using an existing object as a prototype.

     const personPrototype = {
       greet() {
         console.log(
           `Hello, my name is ${this.name} and I'm ${this.age} years old.`,
         );
       },
     };
     
     const person = Object.create(personPrototype);
     person.name = 'John';
     person.age = 30;
     
     person.greet(); // Output: Hello, my name is John and I'm 30 years old.

  4. ES2015 Classes: Defining a blueprint for objects using classes, similar to other programming languages.

     class Person {
       constructor(name, age) {
         this.name = name;
         this.age = age;
       }
       greet = function () {
         console.log(
           `Hello, my name is ${this.name} and I'm ${this.age} years old.`,
         );
       };
     }
     
     const person = new Person('John', 30);
     person.greet(); // Output: Hello, my name is John and I'm 30 years old.

  5. Constructor Functions: Reusable blueprints for objects, using the new keyword to create instances.

     // Constructor function
     function Person(name, age) {
       this.name = name;
       this.age = age;
       this.greet = function () {
         console.log(
           `Hello, my name is ${this.name} and I'm ${this.age} years old.`,
         );
       };
     }
     
     const person = new Person('John', 30);
     person.greet(); // Output: Hello, my name is John and I'm 30 years old.

  Note: Constructor functions are less commonly used now that ES2015 classes are widely supported.

  17. What is the definition of a higher-order function?

  A higher-order function is a function that:

  1. Takes another function as an argument: A function that accepts another function as a parameter.

     function greet(name) {
       return `Hello, ${name}!`;
     }
     
     function greetName(greeter, name) {
       console.log(greeter(name));
     }
     
     greetName(greet, 'Alice'); // Output: Hello, Alice!

  2. Returns a function as its result: A function that returns another function as its output.

     function multiplier(factor) {
       return function (num) {
         return num * factor;
       };
     }
     
     const double = multiplier(2);
     
     console.log(double(5)); // Output: 10

  In other words, a higher-order function is a function that operates on other functions, either by taking them as input or by producing them as output.

  18. What are the differences between ES2015 classes and ES5 function constructors?

  ES5 Function Constructors

  Uses function constructors and prototypes.

  • Example:

    function Person(name, age) {
      this.name = name;
      this.age = age;
    }
    
    Person.prototype.greet = function () {
      console.log(
        'Hello, my name is ' +
          this.name +
          ' and I am ' +
          this.age +
          ' years old.',
      );
    };
    
    var person1 = new Person('John', 30);
    person1.greet(); // Hello, my name is John and I am 30 years old.

  ES2015 Classes

  Uses the class syntax, making code more readable and adding features.

  • Example:

    class Person {
      constructor(name, age) {
        this.name = name;
        this.age = age;
      }
    
      greet() {
        console.log(
          `Hello, my name is ${this.name} and I am ${this.age} years old.`,
        );
      }
    }
    
    const person1 = new Person('John', 30);
    person1.greet(); // Hello, my name is John and I am 30 years old.

    Key differences

    Syntax and Readability

    • ES5: Function constructors and prototypes
    • ES2015: class keyword, more concise and easier to understand

    Static Methods

    • ES5: Added directly to the constructor function
    • ES2015: Defined within the class using static keyword

    Inheritance

    • ES5: Using Object.create() and manual prototype chain setting
    • ES2015: Using extends keyword, simpler and more intuitive

    Super Calls

    • ES5: Manual parent constructor function call
    • ES2015: Using super keyword to call parent class's constructor and methods

  19. Describe event bubbling

  Event bubbling is a mechanism in the DOM (Document Object Model) where an event, such as a click, is first triggered on the target element and then propagates upward through the DOM tree to the root of the document.

  Bubbling Phase:

  • Description: During the bubbling phase, the event starts at the target element and bubbles up through its ancestors in the DOM hierarchy. Event handlers attached to the target element and its ancestors can all potentially receive and respond to the event.

  • Example:

    // HTML:
    // <div id="parent">
    //   <button id="child">Click me!</button>
    // </div>
    const parent = document.getElementById('parent');
    const child = document.getElementById('child');
    
    parent.addEventListener('click', () => {
      console.log('Parent element clicked');
    });
    
    child.addEventListener('click', () => {
      console.log('Child element clicked');
    });

    When you click the Click me! button, both the child and parent event handlers will be triggered due to event bubbling.

  Stopping Event Bubbling:

  • Method: Use stopPropagation() to stop the event from bubbling up the DOM tree.

  • Example:

    child.addEventListener('click', (event) => {
      console.log('Child element clicked');
      event.stopPropagation();
    });

  20. Describe event capturing

  Event capturing is a propagation mechanism in the DOM where an event, such as a click, is first triggered at the root of the document and then flows down through the DOM tree to the target element.

  Event Propagation Phases:

  1. Capturing Phase: The event moves down from the root to the target element.
  2. Target Phase: The event reaches the target element.
  3. Bubbling Phase: The event bubbles up from the target element back to the root.

  Enabling Event Capturing:

  • Event capturing is disabled by default.
  • Enable it by passing { capture: true } as the third argument to addEventListener().

  Example:

  // HTML:
  // <div id="parent">
  //   <button id="child">Click me!</button>
  // </div>
  const parent = document.getElementById('parent');
  const child = document.getElementById('child');
  
  parent.addEventListener(
    'click',
    () => {
      console.log('Parent element clicked (capturing)');
    },
    true, // Enable capturing phase
  );
  
  child.addEventListener('click', () => {
    console.log('Child element clicked');
  });

  When you click the Click me! button, the parent element's capturing handler will be triggered before the child element's handler.

  Stopping Propagation:

  • Use stopPropagation() to prevent the event from traveling further down the DOM tree during the capturing phase.

  • Example:

    parent.addEventListener(
      'click',
      (event) => {
        console.log('Parent element clicked (capturing)');
        event.stopPropagation(); // Stop event propagation
      },
      true,
    );
    
    child.addEventListener('click', () => {
      console.log('Child element clicked');
    });

  In this example, only the parent event listener will be called when you click the "Click me!" button, as the event propagation is stopped at the parent element.

  21. What is the difference between mouseenter and mouseover event in JavaScript and browsers?

  mouseenter

  • Does not bubble
  • Triggered only when the mouse pointer enters the element itself, not its descendants
  • Only triggered once upon entry of parent element, without regard for its contents

  mouseover

  • Bubbles up the DOM tree
  • Triggered when the mouse pointer enters the element or one of its descendants
  • Can result in multiple event callbacks fired if there are child elements

  22. Explain the difference between synchronous and asynchronous functions

  Synchronous Functions

  • Execute in a sequential order, one after the other
  • Blocking, meaning the program execution halts until the current operation finishes
  • Follow a strict sequence, executing instructions line by line
  • Easier to understand and debug since the flow is predictable
  • Examples: reading files synchronously, looping over large datasets

  Example:

  const fs = require('fs');
  const data = fs.readFileSync('large-file.txt', 'utf8');
  console.log(data); // Blocks until file is read
  console.log('End of the program');

  Asynchronous Functions

  • Do not block the execution of the program
  • Allow other operations to continue while waiting for a response or completion of a time-consuming task
  • Non-blocking, enabling concurrent execution and improving performance and responsiveness
  • Commonly used for tasks like network requests, file I/O, and timers
  • Examples: network requests, user input and events, timers, and animations

  Example:

  console.log('Start of the program');
  
  fetch('https://api.example.com/data')
    .then((response) => response.json())
    .then((data) => console.log(data)) // Non-blocking
    .catch((error) => console.error(error));
  
  console.log('End of program');

  23. Explain AJAX in as much detail as possible

  AJAX is a set of web development techniques using various web technologies on the client side to create asynchronous web applications. Unlike traditional web applications where each user interaction triggers a full page reload, AJAX allows web applications to send data to and retrieve data from a server asynchronously without interfering with the display and behavior of the existing page. This enables dynamic updates to the web page without the need to reload it.

  Key Points:

  • Asynchronous: AJAX enables web applications to update parts of a web page without reloading the whole page.
  • Data Formats: Initially used XML, but JSON is now more common due to its compatibility with JavaScript.
  • APIs: Traditionally used XMLHttpRequest, but fetch() is now preferred for modern web applications.

  XMLHttpRequest API

  Example:

  let xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function () {
    if (xhr.readyState === XMLHttpRequest.DONE) {
      if (xhr.status === 200) {
        console.log(xhr.responseText);
      } else {
        console.error('Request failed: ' + xhr.status);
      }
    }
  };
  xhr.open('GET', 'https://jsonplaceholder.typicode.com/todos/1', true);
  xhr.send();

  • Flow: Creates a new XMLHttpRequest, sets up a callback function to handle state changes, opens a request to a URL, and sends the request.

  fetch() API

  Example:

  fetch('https://jsonplaceholder.typicode.com/todos/1')
    .then((response) => {
      if (!response.ok) {
        throw new Error('Network response was not ok');
      }
      return response.json();
    })
    .then((data) => console.log(data))
    .catch((error) => console.error('Fetch error:', error));

  • Flow: Initiates a fetch request, handles the response with .then() to parse JSON data, and manages errors with .catch().

  How AJAX Works with fetch

  1. Making a Request

  • fetch() initiates an asynchronous request to fetch a resource from a URL.

  • Example:

    fetch('https://api.example.com/data', {
      method: 'GET', // or 'POST', 'PUT', 'DELETE', etc.
      headers: {
        'Content-Type': 'application/json',
      },
    });

  2. Return a Promise

  • fetch() returns a Promise that resolves to a Response object representing the server's response.

  3. Handling the Response

  • The Response object offers methods to handle the body content, such as .json(), .text(), .blob().

  • Example:

    fetch('https://api.example.com/data')
      .then((response) => response.json())
      .then((data) => console.log(data))
      .catch((error) => console.error('Error:', error));

  4. Asynchronous Nature

  • fetch() is asynchronous, allowing the browser to continue executing other tasks while waiting for the server response.
  • Promises (.then(), .catch()) are handled in the microtask queue as part of the event loop.

  5. Request Options

  • The optional second argument to fetch() configures various request aspects, such as HTTP method, headers, body, credentials, and caching.

  6. Error Handling

  • Errors (e.g., network failures, invalid responses) are caught and propagated through the Promise chain using .catch() or try/catch with async/await.

  24. What are the advantages and disadvantages of using AJAX?

  AJAX (Asynchronous JavaScript and XML) enables web pages to send and retrieve data asynchronously, allowing for dynamic updates without full page reloads.

  Advantages

  • AJAX provides a seamless user experience by updating content without full page reloads.
  • It reduces server load and improves performance by only fetching necessary data.
  • AJAX maintains user interactions and client states within the page.

  Disadvantages

  • AJAX relies on JavaScript, which can break functionality if disabled.
  • Dynamic content makes bookmarking specific page states challenging.
  • Search engines may struggle to index dynamic content, posing SEO challenges.
  • Processing AJAX data on low-end devices can be slow, raising performance concerns.

  25. What are the differences between XMLHttpRequest and fetch()?

  Both XMLHttpRequest (XHR) and fetch() enable asynchronous HTTP requests in JavaScript, but differ in syntax, handling, and features.

  Syntax and Usage

  • XMLHttpRequest: Event-driven, requiring event listeners to handle responses and errors.
  • fetch(): Promise-based, offering simpler and more intuitive syntax.

  Request Headers

  • XMLHttpRequest: Set headers using the setRequestHeader method.
  • fetch(): Pass headers as an object in the options parameter.

  Request Body

  • XMLHttpRequest: Send body with the send method.
  • fetch(): Use the body property in the options parameter.

  Response Handling

  • XMLHttpRequest: Use responseType to handle different formats.
  • fetch(): Provides a unified Response object with .then for accessing data.

  Error Handling

  • XMLHttpRequest: Handle errors with onerror event.
  • fetch(): Handle errors using the .catch method.

  Caching Control

  • XMLHttpRequest: Difficult to manage, often requiring workaround methods.
  • fetch(): Supports caching options directly.

  Cancellation

  • XMLHttpRequest: Use the abort() method.
  • fetch(): Use AbortController for request cancellation.

  Progress Support

  • XMLHttpRequest: Supports tracking progress with the onprogress event.
  • fetch(): Does not support native progress tracking.

  Choosing Between Them: fetch() is generally preferred due to its cleaner syntax and promise-based handling, but XMLHttpRequest may still be useful for specific cases like progress tracking.

  26. What are the various data types in JavaScript?

  JavaScript has various data types categorized into two groups: primitive and non-primitive (reference) types.

  Primitive Data Types

  • Number: Represents both integers and floating-point numbers.
  • String: Represents sequences of characters, enclosed in single, double quotes, or backticks.
  • Boolean: Logical entities with values true or false.
  • Undefined: A declared variable without an assigned value.
  • Null: Represents the intentional absence of value.
  • Symbol: A unique, immutable value used as object property keys.
  • BigInt: Represents integers with arbitrary precision, useful for very large numbers.

  Non-Primitive Data Types

  • Object: Used to store collections of data and more complex entities.
  • Array: An ordered collection of data.
  • Function: Functions are objects and can be defined using declarations or expressions.
  • Date: Represents dates and times.
  • RegExp: Represents regular expressions for pattern matching in strings.
  • Map: A collection of keyed data items, allowing keys of any type.
  • Set: A collection of unique values.

  Determining Data Types: JavaScript is dynamically typed, meaning variables can hold different data types over time. Use the typeof operator to determine a variable's type.

  27. What language constructions do you use for iterating over object properties and array items?

  Iterating over object properties and arrays is very common in JavaScript and we have various ways to achieve this. Here are some of the ways to do it:

  Iterating over object

  1. for...in Statement

  Loops over all enumerable properties of an object, including inherited ones.

  for (const property in obj) {
    if (Object.hasOwn(obj, property)) {
      console.log(property);
    }
  }

  2. Object.keys()

  Returns an array of an object's own enumerable property names.

  Object.keys(obj).forEach((property) => console.log(property));

  3. Object.entries()

  Returns an array of a given object's own enumerable string-keyed property [key, value] pairs.

  Object.entries(obj).forEach(([key, value]) =>
    console.log(`${key}: ${value}`),
  );

  4. Object.getOwnPropertyNames()

  Returns an array of all properties (including non-enumerable ones) found directly upon a given object.

  Object.getOwnPropertyNames(obj).forEach((property) =>
    console.log(property),
  );

  Iterating Over Arrays

  1. for Loop

  Traditional loop over array elements.

  for (let i = 0; i < arr.length; i++) {
    console.log(arr[i]);
  }

  2. Array.prototype.forEach()

  Executes a provided function once for each array element.

  arr.forEach((element, index) => console.log(element, index));

  3. for...of Statement

  Loops over iterable objects like arrays.

  for (let element of arr) {
    console.log(element);
  }

  4. Array.prototype.entries()

  Provides both the index and value of each array element in a for...of loop.

  for (let [index, elem] of arr.entries()) {
    console.log(index, ': ', elem);
  }

  28. What are the benefits of using spread syntax and how is it different from rest syntax?

  Spread Syntax

  Introduced in ES2015, the spread syntax (...) is useful for copying and merging arrays and objects without modifying the originals. It's commonly used in functional programming, Redux, and RxJS.

  • Copying Arrays/Objects: Creates shallow copies.

    const array = [1, 2, 3];
    const newArray = [...array]; // [1, 2, 3]
    
    const obj = { name: 'John', age: 30 };
    const newObj = { ...obj, city: 'New York' }; // { name: 'John', age: 30, city: 'New York' }

  • Merging Arrays/Objects: Merges them into a new one.

    const arr1 = [1, 2, 3];
    const arr2 = [4, 5, 6];
    const mergedArray = [...arr1, ...arr2]; // [1, 2, 3, 4, 5, 6]
    
    const obj1 = { foo: 'bar' };
    const obj2 = { qux: 'baz' };
    const mergedObj = { ...obj1, ...obj2 }; // { foo: 'bar', qux: 'baz' }

  • Function Arguments: Passes array elements as individual arguments.

    const numbers = [1, 2, 3];
    Math.max(...numbers); // Same as Math.max(1, 2, 3)

  • Array vs. Object Spreads: Only iterables can be spread into arrays; arrays can be spread into objects.

    const array = [1, 2, 3];
    const obj = { ...array }; // { 0: 1, 1: 2, 2: 3 }

  Rest Syntax

  The rest syntax (...) gathers multiple elements into an array or object, the inverse of the spread syntax.

  • Function Parameters: Collects remaining arguments into an array.

    function addFiveToNumbers(...numbers) {
      return numbers.map((x) => x + 5);
    }
    const result = addFiveToNumbers(4, 5, 6, 7); // [9, 10, 11, 12]

  • Array Destructuring: Collects remaining elements into a new array.

    const [first, second, ...remaining] = [1, 2, 3, 4, 5];
    // first: 1, second: 2, remaining: [3, 4, 5]

  • Object Destructuring: Collects remaining properties into a new object.

    const { e, f, ...others } = { e: 1, f: 2, g: 3, h: 4 };
    // e: 1, f: 2, others: { g: 3, h: 4 }

  • Rest Parameter Rules: Must be the last parameter.

    function addFiveToNumbers(arg1, ...numbers, arg2) {
      // Error: Rest element must be last element.
    }

  29. What is the difference between a Map object and a plain object in JavaScript?

  Map Object

  • Key Types: Allows keys of any type (objects, functions, primitives).
  • Order: Maintains the insertion order of keys.
  • Size: Provides a size property to get the number of key-value pairs.
  • Iteration: Directly iterable, using methods like forEach, keys(), values(), and entries().
  • Performance: Generally better for larger datasets and frequent additions/deletions.

  Plain Object

  • Key Types: Keys are typically strings or symbols. Non-string keys are converted to strings.
  • Order: Insertion order is not guaranteed.
  • Size: No built-in property to get the size. Must manually count the number of keys.
  • Iteration: Not directly iterable. Use methods like Object.keys(), Object.values(), or Object.entries() for iteration.
  • Performance: Faster for small datasets and simple operations.

  Example

  // Map
  const map = new Map();
  map.set('key1', 'value1');
  map.set({ key: 'key2' }, 'value2');
  console.log(map.size); // 2
  
  // Plain Object
  const obj = { key1: 'value1' };
  obj[{ key: 'key2' }] = 'value2';
  console.log(Object.keys(obj).length); // 1 (keys are strings)

  30. What are the differences between Map/Set vs WeakMap/WeakSet?

  The main distinctions between Map/Set and WeakMap/WeakSet in JavaScript are as follows:

  • Key types: Map and Set accept keys of any type (objects, primitive values), whereas WeakMap and WeakSet exclusively use objects as keys, excluding primitive values like strings or numbers.
  • Memory management: Map and Set retain strong references to their keys and values, preventing their disposal by garbage collection. In contrast, WeakMap and WeakSet employ weak references for keys (objects), allowing these objects to be collected by garbage collection if no other strong references persist.
  • Key enumeration: Keys in Map and Set are enumerable and can be iterated over, while those in WeakMap and WeakSet are non-enumerable, precluding retrieval of key or value lists directly from them.
  • Size property: Map and Set possess a size property that indicates the number of elements they contain. In contrast, WeakMap and WeakSet lack a size property because their size may vary as a result of garbage collection.
  • Use cases: Map and Set serve well as general-purpose data structures and for caching purposes. Conversely, WeakMap and WeakSet are primarily suited for storing metadata or additional object-related data without impeding the object's potential garbage collection when no longer needed.

  31. Can you offer a use case for the new arrow => function syntax?

  One practical use case for the arrow function syntax in JavaScript is simplifying callback functions, particularly in scenarios where you need concise, inline function definitions. Here's an example:

  Use Case: Mapping an Array

  Suppose you have an array of numbers and you want to double each number using the map function.

  // Traditional function syntax
  const numbers = [1, 2, 3, 4, 5];
  const doubledNumbers = numbers.map(function (number) {
    return number * 2;
  });
  
  console.log(doubledNumbers); // Output: [2, 4, 6, 8, 10]

  Using arrow function syntax, you can achieve the same result more succinctly:

  // Arrow function syntax
  const numbers = [1, 2, 3, 4, 5];
  const doubledNumbers = numbers.map((number) => number * 2);
  
  console.log(doubledNumbers); // Output: [2, 4, 6, 8, 10]

  32. Explain the concept of a callback function in asynchronous operations

  In asynchronous programming, a callback function is passed as an argument to another function and invoked when a task completes, such as fetching data or handling I/O operations. Here's a concise explanation:

  Example

  function fetchData(callback) {
    setTimeout(() => {
      const data = { name: 'John', age: 30 };
      callback(data);
    }, 1000);
  }
  
  fetchData((data) => {
    console.log(data); // { name: 'John', age: 30 }
  });

  33. Explain the concept of debouncing and throttling

  Debouncing delays function execution until a specified time has passed since its last call, useful for tasks like search input handling.

  function debounce(func, delay) {
    let timeoutId;
    return (...args) => {
      clearTimeout(timeoutId);
      timeoutId = setTimeout(() => func.apply(this, args), delay);
    };
  }

  Throttling limits function execution to at most once within a specified interval, beneficial for tasks like handling frequent events such as window resizing or scrolling.

  function throttle(func, limit) {
    let inThrottle;
    return (...args) => {
      if (!inThrottle) {
        func.apply(this, args);
        inThrottle = true;
        setTimeout(() => (inThrottle = false), limit);
      }
    };
  }

  These techniques optimize performance and manage event-driven behaviors effectively in JavaScript applications.

  34. Explain the concept of destructuring assignment for objects and arrays

  Destructuring assignment simplifies extracting values from arrays or properties from objects into separate variables:

  Example

  // Array destructuring
  const [a, b] = [1, 2];
  
  // Object destructurin
  const { name, age } = { name: 'John', age: 30 };

  This syntax uses square brackets for arrays and curly braces for objects, enabling concise variable assignment directly from data structures.

  35. Explain the concept of hoisting with regards to functions

  Hoisting moves function declarations to the top of their scope during compilation, allowing them to be called before their actual placement in the code. Function expressions and arrow functions, however, must be defined before they are called to avoid errors.

  Example

  // Function declaration
  hoistedFunction(); // Works fine
  function hoistedFunction() {
    console.log('This function is hoisted');
  }
  
  // Function expression
  nonHoistedFunction(); // Throws an error
  var nonHoistedFunction = function () {
    console.log('This function is not hoisted');
  };

  36. Explain the concept of inheritance in ES2015 classes

  In ES2015, classes use extends to enable one class to inherit properties and methods from another. The super keyword accesses the parent class's constructor and methods.

  Example

  class Animal {
    constructor(name) {
      this.name = name;
    }
  
    speak() {
      console.log(`${this.name} makes a noise.`);
    }
  }
  
  class Dog extends Animal {
    constructor(name, breed) {
      super(name);
      this.breed = breed;
    }
  
    speak() {
      console.log(`${this.name} barks.`);
    }
  }
  
  const dog = new Dog('Rex', 'German Shepherd');
  dog.speak(); // Output: Rex barks.

  Here, Dog inherits from Animal, showcasing how classes streamline inheritance and method overriding in JavaScript.

  37. Explain the concept of lexical scoping

  Lexical scoping in JavaScript determines variable access based on its position in the source code. Nested functions can access variables from their outer scope.

  Example

  function outerFunction() {
    let outerVariable = 'I am outside!';
  
    function innerFunction() {
      console.log(outerVariable); // 'I am outside!'
    }
  
    innerFunction();
  }
  
  outerFunction();

  Here, innerFunction can access outerVariable due to lexical scoping rules.

  38. Explain the concept of scope in JavaScript

  Scope in JavaScript determines the visibility of variables and functions within different parts of the code. There are three main types: global scope, function scope, and block scope.

  Example

  // Global scope
  var globalVar = 'I am global';
  
  function myFunction() {
    // Function scope
    var functionVar = 'I am in a function';
  
    if (true) {
      // Block scope
      let blockVar = 'I am in a block';
      console.log(blockVar); // Accessible here
    }
  
    // console.log(blockVar); // Throws an error
  }
  
  console.log(globalVar); // Accessible here
  // console.log(functionVar); // Throws an error

  Global scope variables are accessible throughout the code, while function scope variables are limited to the function they are declared in. Block scope, introduced in ES6, confines variables to the block they are declared within (e.g., within curly braces ).

  39. Explain the concept of the spread operator and its uses

  The spread operator (...) in JavaScript expands elements of an iterable (like arrays or objects) into individual elements. It's used for copying arrays or objects, merging them, and passing array elements as function arguments.

  Examples

  // Copying an array
  const arr1 = [1, 2, 3];
  const arr2 = [...arr1];
  
  // Merging arrays
  const arr3 = [4, 5, 6];
  const mergedArray = [...arr1, ...arr3];
  
  // Copying an object
  const obj1 = { a: 1, b: 2 };
  const obj2 = { ...obj1 };
  
  // Merging objects
  const obj3 = { c: 3, d: 4 };
  const mergedObject = { ...obj1, ...obj3 };
  
  // Passing array elements as function arguments
  const sum = (x, y, z) => x + y + z;
  const numbers = [1, 2, 3];
  console.log(sum(...numbers)); // Output: 6

  The spread operator simplifies tasks like copying, merging, and function argument handling by expanding iterable elements into individual components.

  40. Explain the concept of this binding in event handlers

  In JavaScript, the this keyword refers to the object executing the current code. In event handlers, this usually points to the element that triggered the event. However, its value can vary based on how the handler is defined and invoked. To ensure this refers correctly, methods like bind(), arrow functions, or explicit context assignment are used.

  These approaches help maintain the intended context for this within event handling functions, ensuring predictable behavior across different event-triggering scenarios in JavaScript applications.

  41. Explain the difference between classical inheritance and prototypal inheritance

  Classical Inheritance: In languages like Java and C++, classes inherit from other classes through a hierarchical structure. Instances are created from classes using constructors.

  Prototypal Inheritance: In JavaScript, objects inherit directly from other objects. Objects serve as prototypes, and new objects are created based on existing ones.

  Classical inheritance uses classes for instantiation, while prototypal inheritance leverages object linkage for property and behavior inheritance, highlighting JavaScript's unique approach to object-oriented programming.

  42. Explain the difference between document.querySelector() and document.getElementById()

  document.querySelector() selects elements using CSS selectors and returns the first match.

  const element = document.querySelector('.my-class');

  document.getElementById() selects an element by its ID attribute and returns the element with that specific ID.

  const elementById = document.getElementById('my-id');

  While document.querySelector() offers flexibility with CSS selectors, document.getElementById() is straightforward for selecting elements by their unique IDs in the DOM.

  43. Explain the difference between dot notation and bracket notation for accessing object properties

  Dot Notation: Concise and straightforward, it accesses object properties using valid identifiers.

  const obj = { name: 'Alice', age: 30 };
  
  console.log(obj.name); // Alice

  Bracket Notation: Flexible, it accesses properties using strings, suitable for names with special characters or dynamic properties.

  const obj = { name: 'Alice', 'favorite color': 'blue' };
  
  console.log(obj['favorite color']); // blue

  Dot notation is clear for standard properties, while bracket notation handles special cases like dynamic or non-standard property names effectively.

  44. Explain the difference between global scope, function scope, and block scope

  Global Scope

  Accessible from anywhere in the code.

  var globalVar = "I'm global"; // Global scope

  Function Scope

  Limited to the function where it's declared.

  function myFunction() {
    var functionVar = "I'm in a function"; // Function scope
  }

  Block Scope

  Restricted to the block where let or const is used.

  function myFunction() {
    if (true) {
      let blockVar = "I'm in a block"; // Block scope
      console.log(blockVar); // Accessible here
    }
    // console.log(blockVar); // ReferenceError: blockVar is not defined
  }

  These scopes define where variables can be accessed, from global access throughout the code to specific function or block-level access for better control and encapsulation of variables.

  45. Explain the difference between shallow copy and deep copy

  Shallow Copy

  Duplicates top-level properties; nested objects remain referenced.

  let obj1 = { a: 1, b: { c: 2 } };
  let shallowCopy = Object.assign({}, obj1);
  shallowCopy.b.c = 3;
  console.log(obj1.b.c); // 3

  Deep Copy

  Duplicates all levels, creating independent nested objects.

  let deepCopy = JSON.parse(JSON.stringify(obj1));
  deepCopy.b.c = 4;
  console.log(obj1.b.c); // 2

  Shallow copies share references to nested objects, while deep copies create entirely new instances, ensuring independent modifications.

  46. Explain the difference in hoisting between var, let, and const

  var:

  • Hoisted to the top of its scope.
  • Initialized with undefined.
  • Can be used before its declaration without throwing an error.

  console.log(myVar); // undefined
  var myVar = 'Hello';

  let and const:

  • Hoisted to the top of their scope.
  • Not initialized (temporal dead zone).
  • Accessing them before declaration results in a ReferenceError.

  console.log(myLet); // ReferenceError: Cannot access 'myLet' before initialization
  let myLet = 'World';
  
  console.log(myConst); // ReferenceError: Cannot access 'myConst' before initialization
  const myConst = '!';

  const:

  • Requires an initial value at declaration.
  • Once assigned, its value cannot be changed (immutable).

  const PI = 3.14;
  PI = 3.14159; // TypeError: Assignment to constant variable.

  47. How can closures be used to create private variables?

  Closures in JavaScript provide a mechanism to create private variables by encapsulating them within a function scope. Here's how closures can be used to achieve this:

  function createCounter() {
    let count = 0;
  
    return {
      increment: () => ++count,
      decrement: () => --count,
      getCount: () => count,
    };
  }
  
  const counter = createCounter();
  console.log(counter.increment()); // 1
  console.log(counter.getCount()); // 1
  console.log(counter.count); // undefined

  48. How do Sets and Maps handle equality checks for objects?

  Sets and Maps in JavaScript determine the equality of objects based on reference equality, not by comparing their contents. This means objects are considered equal only if they point to the same memory location. For instance:

  const set = new Set();
  const obj1 = { a: 1 };
  const obj2 = { a: 1 };
  
  set.add(obj1);
  set.add(obj2);
  
  console.log(set.size); // Output: 2

  In this example, obj1 and obj2 are treated as separate entries in the Set because they are distinct objects, despite having identical properties. Therefore, Sets and Maps rely on object references to determine equality, not their internal values.

  49. How do you access the index of an element in an array during iteration?

  To access the index of an element in an array during iteration, you can utilize methods like forEach, map, for...of with entries, or a traditional for loop. Here's an example using forEach:

  const array = ['a', 'b', 'c'];
  array.forEach((element, index) => {
    console.log(index, element);
  });

  50. How do you check the data type of a variable?

  To determine the type of a variable in JavaScript, you use typeof followed by the variable name. It returns a string indicating the variable's type: "string", "number", "boolean", "object", "function", "undefined", or "symbol". For arrays, use Array.isArray(variableName), and for null, check variableName === null.

  Conclusion

  You've made it to the end of our extensive list of JavaScript interview questions and answers! We hope this guide has helped you gain the confidence and skills you need to ace your next JavaScript interview. Remember, practice is key, so keep coding and reviewing the concepts until they become second nature.

  Read more

  Open in new tab

• 10 Must-Know JavaScript Coding Interview Questions

  10 essential JavaScript coding interview questions and answers, curated by senior engineers and former interviewers from leading tech companies.

  Level

  Starter

  Tags

  #javascript#interviews

  ---

  Author

  Nitesh Seram

  13 min read

  Sep 28, 2024

  Copy link

  Share

  ---

  As a JavaScript developer, it's essential to be prepared for common interview questions that test your skills and knowledge. Here are 10 must-know questions, along with detailed answers and code examples, to help you ace your next interview.

  1. Debounce

  Debouncing is a crucial technique used to manage repetitive or frequent events, particularly in the context of user input, such as keyboard typing or resizing a browser window. The primary goal of debouncing is to improve performance and efficiency by reducing the number of times a particular function or event handler is triggered; the handler is only triggered when the input has stopped changing.

  Example Usage:

  The debounce function from Lodash can be used to create a debounced version of a function, as shown below:

  import { debounce } from 'lodash';
  
  const searchInput = document.getElementById('search-input');
  
  const debouncedSearch = debounce(() => {
    // Perform the search operation here
    console.log('Searching for:', searchInput.value);
  }, 300);
  
  searchInput.addEventListener('input', debouncedSearch);

  Key Aspects of Debouncing

  • Delays the execution of a function until a certain amount of time has passed since the last input event
  • Helps optimize performance by preventing unnecessary computations or network requests during rapid user input
  • Can be implemented in different versions, including:
    • Leading version: Invokes the callback at the start of the timeout
    • Trailing version: Invokes the callback at the end of the timeout
    • Maximum delay: The maximum time the callback is allowed to be delayed before it is invoked

  Relationship with Throttling

  Debouncing and Throttling are related techniques, but they serve different purposes. Throttling is a technique that limits the frequency of a function's execution, while debouncing delays the execution of a function until a certain amount of time has passed since the last input event.

  Practice implementing a Debounce function on GreatFrontEnd

  2. Promise.all

  Promise.all() is a key feature in JavaScript that simplifies handling multiple asynchronous operations concurrently, particularly when there are dependencies among them. It accepts an array of promises and returns a new promise that resolves to an array of results once all input promises have resolved, or rejects if any input promise rejects.

  Being proficient with Promise.all() demonstrates a front-end engineer's capability to manage complex asynchronous workflows efficiently and handle errors effectively, which is crucial for their daily tasks.

  const promise1 = fetch('https://api.example.com/data/1');
  const promise2 = fetch('https://api.example.com/data/2');
  const promise3 = fetch('https://api.example.com/data/3');
  
  Promise.all([promise1, promise2, promise3])
    .then((responses) => {
      // This callback runs only when all promises in the array have resolved.
      console.log('All responses:', responses);
    })
    .catch((error) => {
      // Handle any errors from any promise.
      console.error('Error:', error);
    });

  In this example, Promise.all() is used to fetch data from three different URLs concurrently. The .then() block executes only when all three promises resolve. If any promise rejects, the .catch() block handles the error.

  This is a valuable topic for front-end interviews since candidates are often tested on their knowledge of asynchronous programming and their ability to implement polyfills. Promise.all() has related functions like Promise.race() and Promise.any(), which can also be covered in interviews, making it a versatile topic to master.

  Practice implementing Promise.all() on GreatFrontEnd

  3. Deep Equal

  Deep Equal is an essential concept in JavaScript for comparing two objects or arrays to determine if they are structurally identical. Unlike shallow equality, which checks if the references of the objects are the same, deep equality checks if the values within the objects or arrays are equal, including nested structures.

  Here's a basic implementation of a deep equal function in JavaScript:

  function deepEqual(obj1, obj2) {
    if (obj1 === obj2) return true;
  
    if (
      obj1 == null ||
      typeof obj1 !== 'object' ||
      obj2 == null ||
      typeof obj2 !== 'object'
    )
      return false;
  
    let keys1 = Object.keys(obj1);
    let keys2 = Object.keys(obj2);
  
    if (keys1.length !== keys2.length) return false;
  
    for (let key of keys1) {
      if (!keys2.includes(key) || !deepEqual(obj1[key], obj2[key])) return false;
    }
  
    return true;
  }
  
  // Example usage
  const object1 = {
    name: 'John',
    age: 30,
    address: {
      city: 'New York',
      zip: '10001',
    },
  };
  
  const object2 = {
    name: 'John',
    age: 30,
    address: {
      city: 'New York',
      zip: '10001',
    },
  };
  
  console.log(deepEqual(object1, object2)); // true

  In this example, the deepEqual function recursively checks if two objects (or arrays) are equal. It first checks if the two objects are the same reference. If not, it verifies that both are objects and not null. Then, it compares the keys and values recursively to ensure all nested structures are equal.

  This topic is valuable for front-end interviews as it tests a candidate's understanding of deep vs. shallow comparisons, recursion, and handling complex data structures.

  Practice implementing Deep Equal on GreatFrontEnd

  4. Event Emitter

  An EventEmitter class in JavaScript is a mechanism that allows objects to subscribe to, listen for, and emit events when specific actions or conditions are met. This class supports the observer pattern, where an object (the event emitter) keeps a list of dependents (observers) and notifies them of any changes or events. The EventEmitter is also part of the Node.js API.

  // Example usage
  const eventEmitter = new EventEmitter();
  
  // Subscribe to an event
  eventEmitter.on('customEvent', (data) => {
    console.log('Event emitted with data:', data);
  });
  
  // Emit the event
  eventEmitter.emit('customEvent', { message: 'Hello, world!' });

  Creating an EventEmitter class requires an understanding of object-oriented programming, closures, the this keyword, and basic data structures and algorithms. Follow-up questions in interviews might include implementing an API for unsubscribing from events.

  Practice implementing an Event Emitter on GreatFrontEnd

  5. Array.prototype.reduce()

  Array.prototype.reduce() is a built-in method in JavaScript that allows you to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value. This method is highly versatile and can be used for a variety of tasks such as summing numbers, flattening arrays, or grouping objects.

  // Example: Summing numbers in an array
  const numbers = [1, 2, 3, 4, 5];
  const sum = numbers.reduce(function (accumulator, currentValue) {
    return accumulator + currentValue;
  }, 0);
  
  console.log(sum); // Output: 15

  Array.prototype.reduce() is a frequently asked topic in front-end interviews, especially by major tech companies, alongside its sister methods, Array.prototype.map(), Array.prototype.filter(), and Array.prototype.concat(). Modern front-end development often utilizes functional programming style APIs like Array.prototype.reduce(), making it an excellent opportunity for candidates to demonstrate their knowledge of prototypes and polyfills. Although it seems straightforward, there are several deeper aspects to consider:

  • Do you know how to use both the initial and returned values of the accumulator?
  • How does the method handle sparse arrays?
  • Are you familiar with the four parameters accepted by the reduce callback function?
  • What happens if the array is mutated during the reduction process?
  • Can you implement a polyfill for Array.prototype.reduce()?

  Practice implementing the Array.prototype.reduce() function on GreatFrontEnd

  6. Flatten

  In JavaScript, "flattening" refers to the process of converting a nested array into a single-level array. This is useful for simplifying data structures and making them easier to work with. JavaScript provides several ways to flatten arrays, with the most modern and convenient method being the Array.prototype.flat() method introduced in ES2019.

  // Example: Flattening a nested array
  const nestedArray = [1, [2, [3, [4, [5]]]]];
  const flatArray = nestedArray.flat(Infinity);
  
  console.log(flatArray); // Output: [1, 2, 3, 4, 5]

  In this example, the flat() method is used with a depth of Infinity to completely flatten the deeply nested array into a single-level array. The flat() method can take a depth argument to specify the level of flattening if the array is not deeply nested.

  Before ES2019, flattening arrays required custom implementations or the use of libraries like Lodash. Here’s a basic custom implementation using recursion:

  // Custom implementation of flattening an array
  function flattenArray(arr) {
    return arr.reduce((acc, val) => {
      return Array.isArray(val) ? acc.concat(flattenArray(val)) : acc.concat(val);
    }, []);
  }
  
  const nestedArray = [1, [2, [3, [4, [5]]]]];
  const flatArray = flattenArray(nestedArray);
  
  console.log(flatArray); // Output: [1, 2, 3, 4, 5]

  This custom flattenArray function uses the reduce() method to concatenate values into a single array, recursively flattening any nested arrays encountered.

  Practice implementing Flatten function on GreatFrontEnd

  7. Data Merging

  Data merging in JavaScript involves combining multiple objects or arrays into a single cohesive structure. This is often necessary when dealing with complex data sets or integrating data from different sources. JavaScript provides several methods to merge data, including the spread operator, Object.assign(), and various array methods.

  Merging Objects

  Using the Spread Operator

  The spread operator (...) is a concise way to merge objects. It creates a new object by copying the properties from the source objects.

  const obj1 = { a: 1, b: 2 };
  const obj2 = { b: 3, c: 4 };
  
  const mergedObj = { ...obj1, ...obj2 };
  
  console.log(mergedObj); // Output: { a: 1, b: 3, c: 4 }

  In this example, obj2's b property overwrites obj1's b property in the merged object.

  Using Object.assign()

  Object.assign() is another method to merge objects. It copies all enumerable properties from one or more source objects to a target object.

  const obj1 = { a: 1, b: 2 };
  const obj2 = { b: 3, c: 4 };
  
  const mergedObj = Object.assign({}, obj1, obj2);
  
  console.log(mergedObj); // Output: { a: 1, b: 3, c: 4 }

  Merging Arrays

  Using the Spread Operator

  The spread operator can also merge arrays by concatenating them.

  const array1 = [1, 2, 3];
  const array2 = [4, 5, 6];
  
  const mergedArray = [...array1, ...array2];
  
  console.log(mergedArray); // Output: [1, 2, 3, 4, 5, 6]

  Using Array.concat()

  The concat() method merges two or more arrays into a new array.

  const array1 = [1, 2, 3];
  const array2 = [4, 5, 6];
  
  const mergedArray = array1.concat(array2);
  
  console.log(mergedArray); // Output: [1, 2, 3, 4, 5, 6]

  Deep Merging

  For deep merging, where nested objects and arrays need to be merged, a custom function or a library like Lodash can be used. Here's a simple custom implementation:

  function deepMerge(target, source) {
    for (const key in source) {
      if (source[key] instanceof Object && key in target) {
        Object.assign(source[key], deepMerge(target[key], source[key]));
      }
    }
    Object.assign(target || {}, source);
    return target;
  }
  
  const obj1 = { a: 1, b: { x: 10, y: 20 } };
  const obj2 = { b: { y: 30, z: 40 }, c: 3 };
  
  const mergedObj = deepMerge(obj1, obj2);
  
  console.log(mergedObj); // Output: { a: 1, b: { x: 10, y: 30, z: 40 }, c: 3 }

  Using Lodash merge

  Lodash is a popular utility library in JavaScript that provides many helpful functions, including merge. The _.merge function in Lodash recursively merges properties of the source objects into the destination object, which is particularly useful for deep merging of nested objects.

  const _ = require('lodash');
  
  const obj1 = { a: 1, b: { x: 10, y: 20 } };
  const obj2 = { b: { y: 30, z: 40 }, c: 3 };
  
  const mergedObj = _.merge({}, obj1, obj2);
  
  console.log(mergedObj); // Output: { a: 1, b: { x: 10, y: 30, z: 40 }, c: 3 }

  In this example, _.merge deep merges obj1 and obj2, ensuring that nested properties are combined correctly.

  Practice implementing Data Merging function on GreatFrontEnd

  8. getElementsByClassName

  In JavaScript, getElementsByClassName is a method used to select elements from the DOM (Document Object Model) based on their CSS class names. It returns a live HTMLCollection of elements that match the specified class name(s).

  Basic Usage

  You can use getElementsByClassName by calling it on the document object and passing one or more class names as arguments:

  // Select all elements with the class name "example"
  const elements = document.getElementsByClassName('example');
  
  // Loop through the selected elements
  for (let i = 0; i < elements.length; i++) {
    console.log(elements[i].textContent);
  }

  Multiple Class Names

  You can specify multiple class names separated by spaces:

  const elements = document.getElementsByClassName('class1 class2');

  This will select elements that have both class1 and class2.

  Live HTMLCollection

  The HTMLCollection returned by getElementsByClassName is live, meaning it updates automatically when the DOM changes. If elements with the specified class name are added or removed, the collection is updated accordingly.

  Alternative Methods

  querySelectorAll

  For more complex selections based on CSS selectors, including class names, IDs, attributes, etc., querySelectorAll provides more flexibility:

  const elements = document.querySelectorAll('.example');

  Practice implementing getElementsByClassName on GreatFrontEnd

  9. Memoize

  Memoization is a technique used in programming to optimize expensive function calls by caching their results. In JavaScript, memoization involves storing the results of expensive function calls and returning the cached result when the same inputs occur again.

  The basic idea behind memoization is to improve performance by avoiding redundant calculations. Here’s a simple example of memoization in JavaScript:

  function expensiveOperation(n) {
    console.log('Calculating for', n);
    return n * 2;
  }
  
  // Memoization function
  function memoize(func) {
    const cache = {};
  
    return function (n) {
      if (cache[n] !== undefined) {
        console.log('From cache for', n);
        return cache[n];
      } else {
        const result = func(n);
        cache[n] = result;
        return result;
      }
    };
  }
  
  const memoizedExpensiveOperation = memoize(expensiveOperation);
  
  console.log(memoizedExpensiveOperation(5)); // Output: Calculating for 5, 10
  console.log(memoizedExpensiveOperation(5)); // Output: From cache for 5, 10
  console.log(memoizedExpensiveOperation(10)); // Output: Calculating for 10, 20
  console.log(memoizedExpensiveOperation(10)); // Output: From cache for 10, 20

  How Memoization Works

  • Caching Results: The memoize function wraps around expensiveOperation and maintains a cache object.

  • Cache Check: Before executing expensiveOperation, memoize checks if the result for a given input (n) is already stored in the cache.

  • Returning Cached Result: If the result is found in the cache, memoize returns it directly without re-executing expensiveOperation.

  • Storing Result: If the result is not in the cache, memoize computes it by calling expensiveOperation(n), stores the result in the cache, and then returns it.

  In modern JavaScript, libraries like Lodash provide utilities for memoization, making it easier to apply this optimization technique across different functions and use cases.

  Practice implementing Memoize function on GreatFrontEnd

  10. Get

  Before the introduction of optional chaining (?.) in JavaScript, accessing nested properties in an object could lead to errors if any part of the path did not exist.

  For example:

  const user = {
    name: 'John',
    address: {
      street: '123 Main St',
    },
  };
  
  const city = user.address.city; // throws an error because address.city is undefined

  Using get from Lodash

  To avoid this, developers used workarounds like the get function from Lodash to access nested properties within objects with ease:

  const user = {
    name: 'John',
    address: {
      city: 'New York',
    },
  };
  
  console.log(_.get(user, 'address.city')); // 'New York'
  console.log(_.get(user, 'address.street')); // 'undefined'

  Here, _.get retrieves the value located at obj.user.address.city, handling potential undefined values gracefully.

  However, with the introduction of optional chaining (?.) in JavaScript, we can now access nested properties in a safer way:

  const user = {
    name: 'John',
    address: {
      street: '123 Main St',
    },
  };
  
  const city = user.address?.city; // returns undefined instead of throwing an error

  The ?. operator allows us to access properties in a way that stops evaluating the expression if any part of the path is null or undefined, preventing errors and returning undefined instead.

  Practice implementing get function on GreatFrontEnd

  Conclusion

  These questions cover essential concepts in JavaScript, and understanding them will help you tackle more complex problems in your interviews. Remember to practice and be ready to explain your thought process and code examples!

  Read more

  Open in new tab

• Leveraging Actions in React 19 for Enhanced Form Handling

  Dive into the new actions hooks in React 19 to improve how we can write forms in React.

  Level

  Intermediate

  Tags

  #react

  ---

  Author

  Vikas Yadav

  9 min read

  Aug 10, 2024

  Copy link

  Share

  ---

  

  If you have used Next.js, you have probably heard of Server Actions as a new way to handle form submissions and data mutations in Next.js applications. Server Actions have both server-side and client-side aspects to them and Actions, the client-side APIs are landing in React 19! React Actions are not specific to Next.js or data fetching – they can be used with other server-side frameworks for any asynchronous operations.

  In this post, we will elaborate on what React Actions are and how to use the new hooks like useActionState and useFormStatus to build form submission experiences the modern way.

  Note: As of writing, React 19 has not been published and the API can be prone to updates, so you should always refer to the latest version of the documentation.

  Actions in HTML forms

  Before we dive deeper into React Actions, we should first understand the action property in native HTML forms. Before JavaScript was introduced, the common way to send the data to the server was via the action attribute on <form>s.

  When we define a <form> element, we can also set an action attribute to a URI which will be used as the endpoint to send the data to the server. The action attribute is often combined with method attribute which can be set to HTTP methods like GET or PUT.

  <form action="/user" method="POST">
    <input name="name" id="name" value="" />
    <div>
      <button type="submit">Save</button>
    </div>
  </form>

  When a user clicks on the "Save" button, the browser will make a HTTP request to the /user endpoint using the specified HTTP method. This is a very powerful pattern that does not rely on JavaScript, however there are downsides of this approach:

  1. It results in a full-page refresh
  2. Form states like loading and error cannot be displayed

  Form submissions in React

  Submitting forms in React is straightforward. It can be done by utilizing the onSubmit prop and fetch API. We can show loading and error states through usage of the useState hook and onSubmit prop.

  import { useState } from 'react';
  
  export default function UserForm() {
    const [isPending, setIsPending] = useState(false);
    const [error, setError] = useState(null);
  
    const handleSubmit = async (event) => {
      event.preventDefault();
      const data = new FormData(event.target);
  
      try {
        setError(false);
        setIsPending(true);
  
        await fetch('/user', {
          method: 'POST',
          body: JSON.stringify(data),
        });
        event.target.reset();
      } catch (err) {
        setError(err.message);
      } finally {
        setIsPending(false);
      }
    };
  
    return (
      <form onSubmit={handleSubmit}>
        <input id="name" name="name" />
        {error && <p>{error}</p>}
        <button type="submit">{isPending ? 'Saving...' : 'Save'}</button>
      </form>
    );
  }

  Client-side form submissions and updates offer several advantages, particularly in terms of user experience and performance:

  • Server requests made without a full-page refresh, which results in faster feedback.
  • Show different form states like loading and error – better user experience.

  While client-side form submissions and updates provide numerous benefits, there are also potential problems and pitfalls that we should be aware of:

  • Need to remember to use event.preventDefault otherwise the browser will do a full page refresh on submission of the form.
  • Boilerplate code is required to manually manage the form state.
  • Requires JavaScript to run.

  React Actions

  Enter the era of new React APIs! With the introduction of Actions in React 19, we can harness the power of form actions on the client side as well.

  How to use React Actions in forms

  Typically, HTML <form>s support URI strings for values to the action attribute. However, <form>'s in React 19 accept functions as valid values for the action prop! We can even pass in async functions to the action. When a string is passed to the action, the <form> will behave like native HTML forms, however if a function is passed, the form will be enhanced by React.

  <form action={actionFunction}>

  Let's convert the form above to use React 19's Actions:

  import { useState } from 'react';
  
  export default function UserForm() {
    const [isPending, setIsPending] = useState(false);
    const [error, setError] = useState(null);
  
    async function createUserAction(formData) {
      setError(false);
      setIsPending(true);
      try {
        await fetch('/user', {
          method: 'POST',
          body: JSON.stringify({ name: formData.get('name') }),
        });
  
        alert('User has been created successfully');
      } catch (err) {
        setError(err.message);
      } finally {
        setIsPending(false);
      }
    }
  
    return (
      <form action={createUserAction}>
        <input id="name" name="name" />
        {error && <p>{error}</p>}
        <button type="submit">{isPending ? 'Saving...' : 'Save'}</button>
      </form>
    );
  }

  React does a few special things under the hood when we pass a function to action:

  1. We do not need to worry about calling event.preventDefault(), React does this automatically if a function is passed to action
  2. The action function will receive FormData as a parameter, so we do not need to construct form data ourselves via new FormData(event.target)
  3. Uncontrolled input components within the <form> will be reset upon action success

  That's useful, but do we still have to maintain the pending and error state variables ourselves? Not at all, React also has a solution for them. These issues are addressed by the introduction of new hooks – useActionState and useFormStatus. Let's look at these two new hooks.

  useActionState hook

  The useActionState hook helps make the common cases easier for Actions. useActionState hook accepts multiple parameters:

  • actionFn: A function which will be used as action for the form. actionFn accepts two parameters: previousState and formData
  • initialState: Value to be used as the initial state. It is ignored after the action is first invoked
  • permalink (optional): A string containing the unique page URI that this form modifies

  The useActionState hook returns an array containing two values:

  • formState: A value which will be derived from return value of action function. Defaults to initialState
  • formAction: Reference to action function which was passed to the <form>'s action

  const [state, formAction] = useActionState(actionFn, initialState);

  Let's rewrite our earlier form example using the useActionState hook:

  import { useActionState } from 'react';
  
  async function createUserAction(prevState, formData) {
    try {
      await fetch('/user', {
        method: 'POST',
        body: JSON.stringify({ name: formData.get('name') }),
      });
    } catch (err) {
      return {
        success: false,
        message: err.message,
      };
    }
  
    return {
      success: true,
      message: 'User created successfully!',
    };
  }
  
  export default function UserForm() {
    const [formState, formAction] = useActionState(createUserAction, null);
  
    return (
      <form action={formAction}>
        <input id="name" name="name" />
        {formState?.success === true && (
          <p className="success">{formState?.message}</p>
        )}
        {formState?.success === false && (
          <p className="error">{formState?.message}</p>
        )}
        <button type="submit">Save</button>
      </form>
    );
  }

  A little better! We no longer need a state just for the error message, it is now part of the action state. Astute readers will notice that this new example does not handle the pending/loading states. That's where the useFormStatus hook comes in.

  useFormStatus hook

  The useFormStatus hook provides status information of the last form submission, which can be used by components to render pending states (e.g. loading indicators, disabling buttons and inputs).

  It does not accept any parameters and returns a status object with the following properties:

  • pending: A boolean value that indicates whether the parent <form> is pending submission
  • data: A FormData object containing data of the parent <form>. It is null if there is no submission or no parent <form>
  • method: A string value of either get or post. This tells us whether the form is getting submitted using GET or POST
  • action: A reference to the action prop on the parent <form>. It is null if there is no parent <form> or if a string URI value provided to the action prop

  const { pending, data, method, action } = useFormStatus();

  Using the useFormStatus hook comes with a caveat – useFormStatus() will only return status information for a parent <form>. It will not return status information for any <form> rendered in that same component or children components. Hence the useFormStatus hook must be called from a component that is rendered inside a <form>.

  Let's rewrite our example to use useFormStatus for handling pending states:

  import { useActionState } from 'react';
  import { useFormStatus } from 'react-dom';
  
  async function createUserAction(prevState, formData) {
    try {
      await fetch('/user', {
        method: 'POST',
        body: JSON.stringify({ name: formData.get('name') }),
      });
    } catch (err) {
      return {
        success: false,
        message: err.message,
      };
    }
  
    return {
      success: true,
      message: 'User created successfully!',
    };
  }
  
  // In order for `useFormStatus` to work we have to extract the button
  // into a separate component so the <form> is now a parent component.
  function SubmitButton() {
    const { pending } = useFormStatus();
  
    return <button type="submit">{pending ? 'Saving...' : 'Save'}</button>;
  }
  
  export default function UserForm() {
    const [formState, formAction] = useActionState(createUserAction, null);
  
    return (
      <form action={formAction}>
        <div>
          <input id="name" name="name" />
        </div>
        {formState?.success === true && (
          <p className="success">{formState?.message}</p>
        )}
        {formState?.success === false && (
          <p className="error">{formState?.message}</p>
        )}
        <SubmitButton />
      </form>
    );
  }

  In order for useFormStatus hook to work, we have to extract the <button> into a separate component so the <form> is now a parent component.

  By using the new useActionState and useFormStatus hooks:

  • There is no need to manually maintain pending status. We can utilize the pending field from the return value of useFormStatus. There is no need to do prop drilling or use context for passing the pending state.
  • The returned state can contain success and error fields from the action function and be used to display success and error messages.

  React Actions gotchas

  • When a <form> action succeeds, React will automatically reset the form for uncontrolled components. If you need to reset the <form> manually, a new requestFormReset React DOM API is available.
  • When a function is passed as the action or formAction props of <form>, <input>, and <button> elements, the HTTP method will be POST regardless of the value of the method prop.
  • The action prop can be overridden by a formAction prop on a <button> or <input> component as these support the formAction prop.

  Conclusion

  The new React Actions, along with the useActionState and useFormStatus hooks provide apps with a new way to write form submissions in React efficiently and can easily manage the form's pending, success, and error states.

  Say goodbye to form boilerplate code!

  Read more

  Open in new tab

• Implementing Code Splitting and Lazy Loading in React

  Learn how to implement Code Splitting and Lazy Loading in React and it's importance.

  Level

  Intermediate

  Tags

  #performance#react

  ---

  Author

  Nitesh Seram

  8 min read

  Jun 3, 2024

  Copy link

  Share

  ---

  

  As Front End Engineers, we aim to deliver the best user experience and one of the ways to achieve that is by optimizing the applications' performance.

  Users expect fast, responsive experiences, and will quickly abandon sites that are slow to load. Studies show that if a web page takes more than 3 seconds to load, over 40% of users will leave. With the prevalent usage of mobile devices which can be on slower network speeds, optimizing performance is critical.

  Code splitting and lazy loading are effective strategies to achieve great performance on the web. In this post, we’ll explore these techniques, their benefits, and how they can be implemented in React.

  Introduction to Code Splitting and Lazy Loading

  Code splitting breaks down your application into smaller chunks, loading only the necessary parts to reduce the bundle size. Lazy loading defers loading non-essential resources until they’re needed, further enhancing performance.

  For example, consider a React app with a Login, Dashboard, and Listing page. Traditionally, the code for all these pages are bundled in a single JS file. This is suboptimal because when the user visits the Login page, it is unnecessary to load pages such as the Dashboard and Listing page. But with implementing code splitting and lazy loading, we can dynamically load specific components/pages only when needed, significantly improving performance.

  In React, code splitting can be introduced via dynamic import(). Dynamic import is a built-in way to do this in JavaScript. The syntax looks like this:

  import('./math').then((math) => {
    console.log(math.add(1, 2));
  });

  For React apps, code splitting using dynamic imports is supported out of the box via React.lazy if a boilerplate like create-react-app is used. The React.lazy() function lets you render a dynamic import as a regular component. This feature was introduced in React 16.6 which allows lazy loading of components via splitting a big JS bundle into multiple smaller JS chunks for each component that is lazily loaded.

  However, if a custom Webpack setup is used, you must check the Webpack guide for setting up code splitting.

  Implementing in React

  To implement lazy loading in React, we can leverage React.lazy function and the Suspense component to handle loading states. Here's an example demonstrating lazy loading in React:

  const LazyComponent = React.lazy(() => import('./LazyComponent'));
  
  function App() {
    return (
      <React.Suspense fallback={<div>Loading...</div>}>
        <LazyComponent />
      </React.Suspense>
    );
  }

  By wrapping a lazy-loaded component with Suspense, we can provide a fallback/placeholder UI while the component is being loaded asynchronously, such as a spinner.

  However, there can be a case where LazyComponent fails to load due to some reason like network failure. In that case, it needs to handle the error smoothly for a better user experience with Error Boundaries.

  import MyErrorBoundary from './MyErrorBoundary';
  const LazyComponent = React.lazy(() => import('./LazyComponent'));
  
  function App() {
    return (
      <MyErrorBoundary>
        <React.Suspense fallback={<div>Loading...</div>}>
          <LazyComponent />
        </React.Suspense>
      </MyErrorBoundary>
    );
  }

  So, when the LazyComponent is lazily loaded, it signifies that the code for LazyComponent is segmented into a distinct JS chunk, separate from the main JS bundle. This JS chunk is exclusively loaded when the LazyComponent is required to be displayed on the user interface, optimizing the loading process and enhancing the application's performance.

  Note: React.lazy and Suspense only work on the client side and are not available for server-side rendering. For server-side code splitting, the loadable/component library can be used.

  From the above, we have seen how we use React.lazy to code split and lazy load components. But the question is where to lazy load and code split. There are approaches like Route-based code splitting and Component-based code splitting.

  Route-based code splitting

  

  Route-based code splitting is almost always the best place to start code splitting and it is also where we can achieve potential max size reduction of our JS bundle. It works best when the routes are very distinct and there is very little code duplication between the routes because if it does there will be duplicate codes in all the JS chunks of lazily-loaded routes. When we try to lazily load all the routes in our app, there is a chance of code duplication in the output bundles. Hence we need to be careful about this when we do code splitting at route level.

  Here is an example of route-based code splitting:

  import { Suspense, lazy } from 'react';
  import { BrowserRouter as Router, Routes, Route } from 'react-router-dom';
  
  const Login = lazy(() => import('./Login'));
  const Dashboard = lazy(() => import('./Dashboard'));
  
  const App = () => (
    <Router>
      <Suspense>
        <Routes>
          <Route path="/" element={<Login />} />
          <Route path="/about" element={<Dashboard />} />
        </Routes>
      </Suspense>
    </Router>
  );

  Component-based code splitting

  

  Component-based code splitting provides granular control over loading specific components, allowing for more precise optimization. The real power of code splitting comes into the picture in component-based code splitting where we have more control over granular components. When deciding which components to lazy load, consider the importance and impact of each component on the initial rendering and user experience. Ideal candidates for lazy loading are large components with significant code or resources, conditional components that are not always needed, and secondary or non-essential features. These can be segmented into separate chunks and loaded on demand, optimizing performance. However, critical components like headers, main content, and dependencies should be loaded upfront to ensure a seamless user experience. We need to be careful in selecting which components to lazy load to strike a balance between initial load times and providing essential functionality. Here is an example of component-based code splitting:

  import { useState, lazy, Suspense } from 'react';
  
  const Modal = lazy(() => import('./Modal'));
  
  function App() {
    const [showModal, setShowModal] = useState(false);
  
    const openModal = () => {
      setShowModal(true);
    };
  
    const closeModal = () => {
      setShowModal(false);
    };
  
    return (
      <div>
        <button onClick={openModal}>Open Modal</button>
        {showModal && (
          <Suspense fallback={<div>Loading Modal...</div>}>
            <Modal onClose={closeModal} />
          </Suspense>
        )}
      </div>
    );
  }
  
  export default App;

  In this example, the Modal component is lazily loaded using React.lazy() and dynamically imported. The modal is conditionally rendered based on the showModal state, which is toggled by the openModal and closeModal functions. The Suspense component displays a loading indicator while the modal component is being loaded asynchronously. This implementation optimizes performance by loading the modal component only when the user interacts with the Open Modal button, preventing unnecessary loading of heavy components like a text editor until they are actually needed.

  Webpack magic comments

  If you’re using Webpack to bundle your application, then you can use Webpack's magic comments to further improve the user experience with lazy loading.

  We can use webpackPrefetch and webpackPreload for dynamic imports. In the above example of the lazy loading Modal, the Modal is loaded only when the user clicks the Open Modal button and the user has to wait for a fraction of a second to load the Modal.

  We can improve the user experience by not making users wait for the Modal to load. So, in that scenario, we can prefetch or preload the Modal component. In the above example of the Lazy loading modal, the only difference will be in how we import the Modal component.

  Before:

  const Modal = lazy(() => import('./Modal'));

  After:

  const Modal = lazy(() => import(/* webpackPrefetch: true */ './Modal'));

  What webpackPrefetch: true does is that it tells the browser to automatically load this component into the browser cache so it's ready ahead of time and the user won’t have to wait for the Modal component to load when the user clicks on the Open Modal button.

  We can use webpackPrefetch and webpackPreload for a particular component when we think that there is a high possibility for the user to use that component when a user visits the app.

  When to use code splitting and lazy loading?

  Use code splitting and lazy loading when:

  • Your application is large and complex, with many components and dependencies.
  • Components are not needed on the initial page load (e.g. below-the-fold, only after interaction).
  • You want to reduce the initial bundle size.
  • Certain components are conditionally rendered or used in specific scenarios.

  Avoid code splitting and lazy loading when:

  • Your application is small and simple, with minimal components.
  • The overhead of managing code splitting outweighs the benefits.
  • Critical components are always needed on the initial load.

  Conclusion

  Be sure to assess your application's requirements, tech stack and challenges when deciding the code splitting and lazy loading approach. By strategically dividing code and loading resources on demand, you can create fast, efficient, and engaging web applications.

  Read more

  Open in new tab

• Image Performance Techniques

  Improve your website's speed and user experience through these image performance techniques.

  Level

  Starter

  Tags

  #resources

  ---

  Author

  Feilin Liangga Putri

  5 min read

  Jun 3, 2024

  Copy link

  Share

  ---

  

  Other than front end performance techniques, image performance is also crucial in developing a web application, especially if your website contains a lot of them. This article contains multiple ways we can do to make image loading more efficient and thus, reduce the time needed to display.

  Content Delivery Network

  Content delivery network (CDN) saves a copy of our web content on many servers around the world. This is to allow content to be delivered to users from their nearest server.

  Benefits

  • Reduce latency
  • Enhance reliability and scalability

  Implementation

  1. Choose a CDN provider.
  2. Set up the CDN by pointing it to the website's static content ie. images.
  3. Update to show images from the CDN's URLs.

  Resources

  • What is a CDN (Content Delivery Network)? | AWS
  • What is a content delivery network (CDN)? How do CDNs work? | Cloudflare

  Optimal Image Formats

  Having optimal image formats, such as WebP or AVIF, can reduce sizes while maintaining quality. These formats use advanced compression techniques, making web pages load faster.

  Benefits

  • Reduce image sizes significantly
  • Maintain high quality

  Implementation

  1. Convert the images to modern formats like WebP or AVIF using conversion tools.
  2. Use <picture> to provide multiple sources in different formats, letting the browser choose the most compatible and efficient one.

  Resources

  • Which is the Best Image Format for Your Website? | ImageKit
  • 13 Best Image Formats and When to Use Them | Hostinger

  Responsive Images

  To have responsive images, where images adjust their own size to the current display size, we can provide multiple sources for the image, allowing the browser to select the most appropriate version.

  Benefits

  • Save bandwidth on smaller devices
  • Improve visual quality on larger screens

  Implementation

  1. Define different image sizes for various screen resolutions and save them.
  2. Use srcset in <img> to list these image sources of different sizes to match various display sizes.

  Resources

  • Responsive images | MDN Web Docs
  • Responsive images | web.dev

  Adaptive Images

  Adaptive images involve detecting network speed and serving different image qualities accordingly. Users with slower connections will receive lower-quality images as compared to those with faster connections.

  Benefits

  • Enhance user experience on slow networks
  • Reduce unnecessary data usage

  Implementation

  1. Implement JS to detect the network condition using the Network Information API.
  2. Based on the network speed, dynamically load and display images of appropriate quality by modifying the source attributes.

  Resources

  • Adaptive images in HTML | Adaptive Images
  • How To Solve Adaptive Images In Responsive Web Design

  Offscreen Image

  Images that are offscreen, or not in the viewport, are not loaded until they are needed. This means that the images are only loaded when they are about to become visible / nearing the viewport.

  Benefits

  • Improve initial page load time
  • Save bandwidth by not loading hidden images

  Implementation

  1. Identify images that are initially offscreen when the page loads.
  2. Use JS or CSS to delay loading these images until they are near the viewport.

  Resources

  • How to Defer Offscreen Images (With and Without Plugins) | Cloudways
  • Defer offscreen images | Chrome for Developers

  Lazy Loading

  With lazy loading, similar to offscreen images, images and iframes are loaded only as they approach the user's viewport. This can significantly reduce initial page load times and save bandwidth.

  Benefits

  • Reduce initial page weight
  • Improve initial load time, especially pages with many images

  Implementation

  1. Add loading="lazy" to <img> and <iframe>.

  Resources

  • Lazy loading | MDN Web Docs
  • Browser-level image lazy loading for the web | web.dev

  Progressive JPEGs

  Progressive JPEGs load in layers, improving in clarity and detail with each layer, so that users see a low-quality version of the image almost immediately, which progressively improves until the image fully loads. This enhances the user experience by providing visual content faster.

  Benefits

  • Improve perceived load time
  • Enhance user engagement with immediate visual feedback

  Implementation

  1. Convert JPEG to progressive format using editing tools or conversion software.

  Resources

  • Progressive JPEG images: What Is It and How It Can Improve Website Performance | Hostinger
  • Progressive jpegs (PJPEG): the key to loading images faster on your website | ImageKit

  Preloading

  Preloading allows us to specify which images should be loaded early, even before the browser encounters the image tags. This is particularly useful for images that are crucial to the user experience but might be discovered late by the browser, such as later sections of the page or carousels.

  Benefits

  • Ensure important images are loaded early
  • Improve performance of above-the-fold content

  Implementation

  1. Identify critical images that should be loaded early in the page life cycle.
  2. Use the <link rel="preload"> in <head> to specify these images, setting as="image".

  Resources

  • Preloading responsive images | Web.dev
  • Preloading optional fonts | Web.dev

  Compression

  Compression reduces file sizes by getting rid of unnecessary data, speeding up loading times. Effective compression balances size and quality, allowing images to load quickly without an obvious loss in quality.

  Benefits

  • Reduce image sizes
  • Speed up loading times

  Implementation

  1. Use compression tools.

  Resources

  • Compression in HTTP - MDN Web Docs
  • Introduction to Brotli Compression | CSS Tricks

  ---

  

  Enhancing image performance requires the combination of various techniques. By applying the above techniques, we can significantly improve the loading speed and efficiency of our web applications. Ultimately, staying updated of the latest trends in image optimization and web standards is essential for remaining competitive in web development.

  Read more

  Open in new tab

• Announcing GreatFrontEnd Projects – A real world projects platform for front end engineers

  Build real world projects to learn with hands-on practice, or to stand out with an awesome portfolio.

  Level

  Starter

  Tags

  #announcements#launch#release

  ---

  Author

  Yangshun Tay

  10 min read

  Apr 30, 2024

  Copy link

  Share

  ---

  

  After months of working hard on this, we are thrilled to finally announce the beta launch of GreatFrontEnd Projects! 🥳️

  At GreatFrontEnd, we strive to create a platform for front end engineers to learn, grow and connect with one another.

  Through scouring countless forums frequented by front end engineers and speaking to our users, we've discovered a common need for a platform where you can develop well-crafted real-world projects – be it to learn something new through hands-on practice, or to build up your portfolio of projects.

  We wanted to build the very best version of such a platform while listening to your needs. We believe we are close to achieving this, and we're excited for you to experience it firsthand.

  What exactly is GreatFrontEnd Projects?

  GreatFrontEnd Projects is a platform for front end engineers to build real-world projects.

  In essence, we provide you with tons of real-world project challenges that you can build.

  For each challenge, you'll have access to everything you need to start coding right away – including professional designs, API specs, starter code and image files.

  

  Just click "Start project", open up your IDE and start coding!

  After you're done, host your project on any service and submit your GitHub repo and site url. This will be published for other users to give you code reviews and feedback.

  

  We will pull your code from GitHub directly onto the platform for instant code reviews by the community, allowing you to receive feedback for your work and gain experience points ("reputation") to track your progress.

  

  By using the platform, you can:

  • Learn: Learn new skills through hands-on practice
  • Showcase: Build portfolio-worthy projects like no other.
  • Build faster: Accumulate a toolkit of reusable components for future personal projects.

  Budget-savvy users will also be happy to know that we are predominantly free, with 80% of our challenges accessible for no cost. We believe in providing the basics for free, including multi-page apps and breakpoint management. You won't be charged for essential features like taking screenshots.

  Our premium charges only apply to advanced features that go beyond the basics, offering an extra boost to your learning and development. Find out more →

  Why should you use GreatFrontEnd Projects?

  1. Designed to help you learn any front end skill faster

  Whether you're a complete beginner hoping to learn front end from scratch, or a senior engineer hoping to learn more modern stacks, our platform was designed to assist you in your learning goals.

  Beginner-friendly to nightmare-level challenges.

  We offer a range of starter level challenges that are specifically designed for beginners. You can begin with these and gradually progress to more advanced challenges as you gain confidence and experience.

  

  Extensive learning resources while building

  As you embark on each challenge, you'll have access to a wealth of resources to support your learning journey. These include detailed guides, solutions, references from fellow users, and community forums. These resources are carefully curated to assist you in understanding and mastering the concepts behind each challenge.

  While other platforms might leave you relying solely on community feedback, our premium plan provides you with practical development guides and solutions written by experienced senior engineers from top tech companies. You'll learn best practices and supercharge your learning by referencing professionally-written code derived from years of experience.

  Complete beginners will also be happy to find guides to help you get started with the very basics, such as starting up your IDE and code repository, or building UI with figma.

  

  Every project builds specific skills

  Every challenge on our platform is detailed with the skills that you would be able to learn after building them. Starting from the simplest challenges, you may find yourself learning basic HTML and CSS. As you move along, you start to learn more advanced skills, such as using UI frameworks like React or Svelte.

  Structured learning with skills roadmap

  

  We also offer a skills roadmap on our platform, which serves as a step-by-step guide to acquire all the fundamental skills required for front-end development, from the very basics to advanced topics.

  

  For each skill, it provides you with a list of curated resources, as well as a recommended order of projects to build.

  Feedback and code reviews

  After completing a project, you'll have the opportunity to receive feedback and code reviews from the community. This feedback is invaluable for your growth as it helps you identify areas for improvement and refine your coding skills.

  We make code reviews easy by displaying your code directly on our platform, eliminating the need for community members to go elsewhere to review your work. This convenience encourages more feedback and collaboration, which means you can expect to receive more feedback for your work.

  

  Gamification and progress tracking

  Our platform includes an advanced gamification system that encourages you to track your progress and take on more challenges. Every productive action you undertake towards building projects or learning new skills will be rewarded with reputation points, continuously motivating you to stay engaged and make steady progress in your learning journey.

  

  Real world project specs

  Our projects were designed with real world project specs meant for professional software engineers. This includes project specs and user stories written by professional product managers, and fully specified UI UX designs by high-end designers.

  This means that whatever you build from day 1 will resemble the kind of work you would be expected to do in a full-time front end engineer job. Moreover, you can be sure that every project you spend time building will form a professional application that can be reused for future projects, or used as part of your portfolio. Learn while building something useful!

  

  2. The most impressive collection of portfolio projects in the market – without building the same as others

  If you're looking to build your portfolio – we've built our platform to ensure that you are well taken care of.

  Professional designs by high-end designers

  For developers seeking to build their portfolios or embark on side projects, our platform allows you to build stunning portfolio projects that were professionally designed by high-end designers. Design is hard – and you'd be able to focus solely on the technical execution.

  

  Personalized portfolio projects

  Furthermore, unlike other challenge platforms, you'd be able to easily construct personalized portfolio projects instead of building the same thing as everyone else.

  Each project within our platform is made up of reusable components which adhere to the same design system, making them inherently modular and compatible with one another. This means you can seamlessly combine components from various projects to construct unique and customized applications for your portfolio. These components cover a diverse range of applications, including Marketing, E-Commerce, Web Apps, Games, and even Portfolios, which means you'd be able to compose a wide variety of apps from them.

  

  Build entire component libraries or design systems to impress recruiters

  Additionally, we offer Component Tracks, which are collections of projects that form component libraries or design systems. This can leave a strong impression on potential employers and recruiters, showcasing your expertise and versatility in building a variety of components for common use cases, which is much more impressive than building individual projects.

  

  3. Every challenge is a reusable, modular component that add to your permanent toolkit for future projects

  

  If you enjoy dedicating your spare time to creating side projects, our platform will be beneficial for you as well. Each challenge you complete contributes to a growing collection of professionally designed, reusable components, allowing you to seamlessly integrate them into any of your personal side projects.

  What are the differences between Free and Premium?

  We provide all of the essentials for free. You will be able to complete 80% of our challenges and even some advanced features that other platforms make premium, such as multi-page apps, breakpoint management and screenshot taking.

  Here are the advanced features you can enjoy as a Premium member:

  1. Access to practical development guides and official solutions

  Each guide and solution was written by big tech senior engineers with best practices derived from years of experience, allowing you to learn techniques and patterns early on in your learning, setting up for a strong foundation.

  2. Access to professionally designed figma files

  Learning how to use design tools like Figma is an important skill for any professional front end developer. Moreover, using the design file helps you in building a more precise solution using design details like font sizes, spacing and colors, eliminating the time that would otherwise be spent on guesswork.

  3. Access to the entire skills roadmap

  Without knowing the domain well, it's hard to know which projects you should build in order to train different aspects of a skill. Our skills roadmap solves that problem by providing a structured roadmap of projects to build to train all the core skills required for front end engineers, all the way from beginner to advanced. While the free plan lets you access only the foundational skills in the skills roadmap, you will get full access to all nodes in the skills roadmap once you purchase any premium plan. This helps you learn skills efficiently without the guesswork.

  4. Access to all component tracks

  Our component tracks are a unique feature where each track is a collection of projects that form a component library or even design system. By building entire component tracks, you showcase your abilities and versatility in building a variety of components for common use cases, which is much more impressive than building individual projects. Moreover, one of our component tracks is a design system, which means you get to build the underlying design system behind all of the projects on our platform, serving as a good foundation for your toolkit of reusable components.

  5. Access to our most impressive projects

  Some of our most impressive projects were designed to teach you (and allow you to showcase) complex and / or modern techniques like full stack or artificial intelligence skills. These are the projects you'd want to reference when building your portfolio to stand out from the crowd of applications.

  With these premium features, you'll save considerable time and effort towards building accurate designs and becoming a highly skilled front-end developer.

  Refer to our pricing plan here for a free vs premium comparison table →

  Beta testers, attention!

  With our Beta launch underway, we're eager to collect insights from our beta testers to enhance our platform further. Should you wish to report a bug or propose new features, feel free to reach out via email at feedback@greatfrontend.com or share your thoughts through our feedback widget ("Chat with us!" on the side of the page).

  Thank You

  This was a significant milestone for such a huge project spanning several months. We would like to express our gratitude to the team that helped make this happen, including:

  • Yangshun Tay for leading the engineering design and efforts, as well as all the engineers who contributed directly to the project – Nitesh Seram, Vikas Yadav, Neo Wei Qing, and Jeff Sieu.
  • Fariz Maulana for leading the very challenging design efforts on the projects platform and projects challenges, as well as designers Chew Kia Hwee, Layo Studio, and Tay Yang Heng.
  • Gina Ng for leading the product planning and roadmap, as well as project managing and Feilin Liangga Putri for QA testing the platform.
  • Nikki Gunarso and Seth Gerald for leading the marketing efforts for product launch.
  • All the community members for making valuable code contributions, improving our documentation, and answering questions on Discord.

  Read more

  Open in new tab

• Front End Performance Techniques

  Improve your website's speed and user experience through these front end performance techniques.

  Level

  Starter

  Tags

  #resources

  ---

  Author

  Feilin Liangga Putri

  6 min read

  Mar 26, 2024

  Copy link

  Share

  ---

  

  A good website is not only just about aesthetic user interface, optimizing its front end performance is equally as important, and in certain domains like e-commerce, checkout conversion performance is highly dependent on website performance.

  This article presents a collection of underutilized yet effective strategies that you can use to improve your website's speed and user experience. These are useful concepts to know for front end system interviews as well as for your day-to-day work!

  List virtualization

  List virtualization is an optimization technique where only the currently visible items in a long list or large dataset are rendered. This method dynamically loads and unloads elements based on the scroll position.

  Benefits

  • Reduce memory usage
  • Reduce initial load time and subsequent
  • Smoother scrolling and interaction, as the browser is not overloaded

  Implementation

  1. Install a virtualization library like react-virtualized.
  2. Wrap list in the virtualization component.
  3. Set the item count and provide a function to render each visible item based on the scroll position.

  Resources

  • React Virtualized Documentation
  • List Virtualization | Patterns.dev

  Bundle/code splitting

  Both bundle and code splitting are optimization techniques in web development that involve dividing a large codebase into smaller chunks, loading only the necessary chunks at any point of time. This can significantly enhance the performance and efficiency of applications, especially those with extensive codebases or complex dependencies.

  Benefits

  • Allow browsers to cache parts of the application independently, reducing the need to re-fetch unchanged code
  • Faster load times and smoother and more responsive application

  Implementation

  1. Use a bundler like Webpack or Vite.
  2. Identify split points (e.g., routes or features).
  3. Use import() for dynamic imports at these points.

  Resources

  • Code Splitting | Webpack
  • Bundle Splitting | Patterns.dev

  Dynamic imports / lazy loading

  By implementing dynamic imports, we import code only on interaction, visibility, or navigation. Similar to that, lazy loading is also a popular design pattern that delays the initialization of an object until when it is actually needed by users. These can help to improve efficiency, especially at times where costly resources are not always utilized.

  Benefits

  • Reduce initial load time
  • Save bandwidth as unnecessary code or resources are not loaded upfront
  • More responsive applications as the browser's workload is much less

  Implementation

  1. Identify components for lazy loading.
  2. Replace their imports with dynamic import() calls.
  3. Use placeholders while components load.

  Resources

  • Dynamic import | MDN Web Docs
  • Lazy loading | MDN Web Docs

  Optimize loading sequence

  Optimal loading sequence prioritizes the loading of essential resources, like CSS, fonts, and above-the-fold content. This method carefully orders the loading process, so critical elements are rendered first, enhancing perceived performance. By doing this, non-essential items are deferred, largely boosting efficiency and user satisfaction, especially during page initialization.

  Benefits

  • Faster perceived load time
  • Efficient use of network and browser resources by loading only what's essential upfront, leading to streamlined resource utilization

  Implementation

  1. Identify critical resources for the initial view.
  2. Use <link rel="preload"> for these resources in the HTML head.
  3. Lazy load non-critical resources.

  Resources

  • Optimizing the Critical Rendering Path | Google Developers
  • Prioritizing content in the browser’s critical rendering path | Web.dev

  Prefetching

  Through the prefetching technique, resources are loaded in the background before they are requested by users. This strategy aims to reduce perceived latency and improve responsiveness by fetching resources ahead of time, based on user behavior patterns or predictive algorithms.

  Benefits

  • Reduce latency
  • Smoother transition between pages or actions
  • Ensure resources are ready before they are needed

  Implementation

  1. Identify resources for future use.
  2. Use <link rel="prefetch"> to instruct the browser to load these in idle time.
  3. Monitor and adjust based on user behavior.

  Resources

  • Prefetching - MDN Web Docs
  • Prefetching resources with rel="prefetch" | Web.dev

  Preloading

  Preloading is where specific resources are identified and loaded early in the page's life cycle, even before the browser requires them. This ensures that critical assets such as scripts, stylesheets, and images are readily available by the time they're needed.

  Unlike prefetching, which depends on future navigation, preloading focuses on the current page, strategically accelerating the availability of high-priority resources that are crucial for the immediate next steps. This is particularly useful for resources that are essential for the initial view or interactive features of a page, ensuring a smoother and faster user experience.

  Benefits

  • Immediate availability of critical resources
  • Enhance performance and improve reliability of critical resources loading process

  Implementation

  1. Determine essential resources for the next steps.
  2. Use <link rel="preload"> for these resources, specifying the type with as.

  Resources

  • Preloading responsive images | Web.dev
  • Preloading optional fonts | Web.dev

  Compression

  Compression is a method that reduces file sizes for faster user delivery by eliminating redundant data. This not only quickens load times for web pages and apps but also cuts down on bandwidth and associated costs, similar to how tree shaking, which will be explained below, removes unused code to streamline bundles.

  Benefits

  • Faster data transfer
  • Reduce bandwidth consumption
  • Lower costs

  Implementation

  1. Enable compression on the web server (e.g., Gzip, Brotli).
  2. Compress static assets during the build process.
  3. Ensure compressed files are served with correct headers.

  Resources

  • Compression in HTTP - MDN Web Docs
  • Introduction to Brotli Compression | CSS Tricks

  Tree shaking

  Tree shaking is an optimization technique used to eliminate unused code from the final bundle before deployment. By analyzing the import and export statements in a module structure, static analysis tools can determine which modules and lines of code are not being utilized and remove them.

  Benefits

  • Smaller bundles enhance load times and performance, using fewer resources overall
  • Better maintainability with a cleaner codebase

  Implementation

  1. Use a bundler that supports tree shaking (e.g., Webpack).
  2. Write code in ES6 modules.
  3. Enable production mode in the bundler to remove unused code.

  Resources

  • Tree Shaking | Webpack
  • Tree Shaking | MDN Web Docs

  ---

  

  Optimizing front end performance is important in providing a fast, efficient, and enjoyable user experience. Techniques mentioned above are often powerful yet often underutilized. By carefully implementing these strategies, we can ensure that our applications perform optimally, keeping users engaged and satisfied.

  Read more

  Open in new tab

• Top 5 CSS Mistakes made by Front End Engineers

  5 most common CSS mistakes Front End Engineers make and how to avoid them.

  Level

  Starter

  Tags

  #css

  ---

  Author

  Jordan Cutler

  10 min read

  Mar 5, 2024

  Copy link

  Share

  ---

  

  This is a guest post by Jordan Cutler, Senior Frontend Engineer at Pinterest and author of the High Growth Engineer Newsletter.

  ---

  I've seen a lot of CSS.

  Unfortunately, there aren't great resources on doing it right.

  In my experience as a Senior Frontend Engineer, I see 5 common mistakes that I'll go over in this article and how to avoid them.

  Recognizing and avoiding these mistakes will help you write CSS that:

  1. Works across devices—not just your laptop
  2. Works the first time you try it
  3. Makes you less frustrated with CSS

  Let's dive in!

  Mistake 1: Using width and height properties incorrectly

  One of the most common mistakes comes at the cost of responsiveness.

  It's the overuse of width and height.

  Luckily, there are easy fixes to this.

  In general:

  • Use max-width alongside width
  • Swap height for min-height

  Using width and height can be ok in certain scenarios. If you are using them, you should know what you're doing and be cautious.

  Some examples where width and height make more sense:

  • An icon that should only be displayed at a particular fixed size.
  • A fixed element on the page, like a sticky nav, footer, or sidebar.
  • A set of elements that you want to become scrollable if the screen is too small by also setting overflow: auto on their parent.

  HTML is responsive by default. Our CSS is what often breaks the responsiveness. When we add styles, we need to keep our page responsive.

  Using width and height is dangerous because they are restrictive.

  It says: "You must be this size no matter what."

  For example: If we use width: 900px on an element, what happens if we are on mobile?

  It would overflow off the screen.

  

  If you do need to use a fixed width value, make it flexible. My preferred way for doing that is adding max-width: 100% .

  

  A common example I see in the real world is defining a fixed width value on <input> elements.

  Here's what it looks like when an <input> is 400px inside a container that was shrunk to 250px.

  

  Once we apply max-width: 100% the issue goes away.

  

  Similarly, we run into the same issue with height.

  If we define a fixed height: 250px and our content size is greater than 250px, we see this happen:

  

  However, the fix is easy. We can use min-height: 250px instead.

  Now, our container will always be at least 250px, but can become larger if it needs to fit the content inside.

  

  Mistake 2: Misunderstanding "layout elements" and "content elements"

  CSS is often considered difficult to maintain.

  A large reason for this is mixing responsibilities in CSS.

  In the same way that you don't want a function to be doing 10 different things, we can apply that principle to our CSS.

  How? By dividing each element we apply CSS to into either a "layout element" or a "content element."

  Here are examples of content elements:

  • A button
  • A text input
  • A paragraph
  • A link in the navbar
  • A card

  Essentially, they are isolated items that hold content.

  In comparison, "layout elements" define the layout those "content elements" should be placed in.

  They define the structure via flexbox, grid, gap, and margin.

  Layout elements are all the elements you don't see.

  Here's an example:

  Let's look at the Tailwind landing page and see how it is structured by adding a border: 1px solid red to everything.

  

  You can already start to see where the "content" elements are vs the "layout elements." The content elements are the buttons, text inputs, paragraph text, icon buttons in the navbar, etc.

  Let's focus on the bottom row with the "Get started" button:

  

  The "Get started" button and "Quick search" input are wrapped in a <div> which is the layout element.

  It defines display: flex, margin-top, and justify-content: center.

  With that, it created the skeleton where content elements can just be plopped into the correct location.

  In your CSS, you should aim to use this pattern too.

  A common mistake would be applying margin-top on one or both of these buttons, rather than letting the layout element do it.

  Mistake 3: Choosing between padding, margin, gap incorrectly

  Question: In the below image, would you use padding, margin, or gap to add space between these tags?

  

  Hopefully, your answer is gap.

  Often, I see something like:

  <style>
    .tag {
      margin-left: 8px;
    }
  
    .tag:first-child {
      margin-left: 0;
    }
  </style>
  
  <div class="tag">All</div>
  <div class="tag">Music</div>
  <div class="tag">JavaScript</div>
  ...
  <div class="tag">Sales</div>

  While this "works", it breaks separation of responsibilities.

  The .tag should just be concerned with rendering itself and its content.

  Instead, we can do:

  <style>
    .tagRow {
    	display: flex;
    	gap: 8px;
    }
  
    .tag {
    	// The CSS that controls the tag appearance
    }
  </style>
  
  <div class="tagRow">
    <div class="tag">All</div>
    <div class="tag">Music</div>
    <div class="tag">JavaScript</div>
    ...
    <div class="tag">Sales</div>
  </div>

  This defines a wrapper around the .tags. Any element inside that tag wrapper will receive a space around them that is 8px wide. The .tag doesn't know anything about and should not bother with the context it's in. It's just a tag being placed in a pre-defined layout.

  What about padding?

  Think of padding as bubble wrap inside a package. It's part of the package, but not the contents.

  Padding is just whitespace that is part of the element itself and prevents the content from being too tightly packed.

  Padding gets applied to "content elements."

  What about margin?

  Think of margin as a restraining order. You have to be a minimum distance away.

  I don't like to apply margin to "content elements."

  Instead, I create a wrapping element that applies the margin.

  For example, let's say we have a button at the bottom of a form like this:

  <form>
    <input />
    <input />
    ...
    <button type="submit">Submit</button>
  </form>

  If we want to add a minimum amount of space above the button and any other content, I'd create a wrapper div around the button to apply that margin.

  <form>
    <input />
    <input />
    ...
  
    <div class="submitButtonWrapper">
      <button type="submit">Submit</button>
    </div>
  </form>
  
  <style>
    .submitButtonWrapper {
      margin-top: 16px;
    }
  </style>

  Technically, you could add the margin to the submit <button> directly. I don't prefer this though.

  In practice, your buttons will usually be abstracted away in a component library that usually prevents style overrides—for good reason.

  By creating this wrapper element, the separation of responsibilities is clearer.

  One more note for a good use of margin: Typography elements.

  Headings and paragraphs are good uses of margin, since there will usually be varying amounts of spacing between these and they usually aren't wrapped in a container where gap makes sense.

  Mistake 4: Not knowing about layout modes

  Let's say we have 2 <div> elements and some CSS like this:

  <style>
    div {
    	width: 100px;
    	height: 100px;
    }
  
    .blue {
    	z-index: 5000;
    	background-color: blue;
    }
  
    .red {
    	z-index: 4000;
    	background-color: red;
    	// Just to get both divs on top of each other
    	margin-top: -100px;
    }
  </style>
  
  <div class="blue"></div>
  <div class="red"></div>

  Do you know which one will be displayed on top?

  …

  The answer is… red.

  Why?

  If you answered blue, you might have thought it was because the z-index of the .blue div was higher.

  While that is true, z-index isn't doing anything here.

  It's not doing anything because z-index only works in certain "layout modes."

  Because it isn't doing anything, the element that appears in the DOM later is rendered at the top. In this case, since the .red div element comes later, it will appear above the other.

  How do we fix this?

  The default layout mode for most elements is called "flow".

  z-index isn't implemented in the "flow" layout mode.

  The MDN docs call this out in the position: static area which is the default for elements.

  

  But it is implemented in "positioned" layout mode.

  

  To enter positioned layout for an element, we can apply position: relative, position: absolute, position: fixed, or position: sticky

  In this case, the easiest way to get z-index to work is to use position: relative.

  <style>
    div {
    	width: 100px;
    	height: 100px;
    }
  
    .blue {
    	position: relative;
    	z-index: 5000;
    	background-color: blue;
    }
  
    .red {
    	position: relative;
    	z-index: 4000;
    	background-color: red;
    	// Just to get both divs on top of each other
    	margin-top: -100px;
    }
  </style>
  
  <div class="blue"></div>
  <div class="red"></div>

  Since both elements are in the "positioned" layout mode, z-index will work and the .blue div will be displayed on top.

  You probably knew this without realizing it

  If you've instinctively used gap only when you add display: flex or display: grid, you probably knew this without realizing it.

  Why don't you just add gap without adding display: flex ?

  Because gap isn't implemented in the default layout mode—flow.

  But it is in the "flex" layout mode! Which you get when you do display: flex.

  Some more quick examples

  • Using top, left, right, bottom only works in "positioned" layout mode.
  • Margin collapsing only works in "flow" layout mode.
  • grid-template-areas only works in "grid" layout mode.

  Mistake 5: Using only grid or only flex

  The final common mistake is overusing only display: grid or only display: flex.

  Although many display: flex cases can use display: grid and vice-versa, each of these excel in their own areas.

  CSS Grid is great for 2-dimensional layouts. I often see good CSS grid use cases when building a page-level layout structure.

  For example, Una Kravetz shares how to build the classic holy grail layout using CSS Grid.

  

  .parent {
    display: grid;
    grid-template: auto 1fr auto / auto 1fr auto;
  }
  
  header {
    grid-column: 1 / 4;
  }
  
  .left-side {
    grid-column: 1 / 2;
  }
  
  main {
    grid-column: 2 / 3;
  }
  
  .right-side {
    grid-column: 3 / 4;
  }
  
  footer {
    grid-column: 1 / 4;
  }

  Flexbox is great for stacking items side by side or on top of each other in 1 dimension.

  A great example of this is something like nav items that should be equally spaced apart.

  Here is an example on Tailwind's home page.

  

  Here's one more example on Airbnb.

  

  In general, I use Flexbox more than CSS Grid, but they both have their use cases and its important to use the correct one for your use case.

  To learn more about Flexbox and CSS Grid on a fundamental level, I recommend Josh Comeau's Interactive Flexbox Guide and his Interactive CSS Grid Guide.

  Conclusion

  

  These are the top 5 CSS mistakes I've seen in my experience, but I'm sure there are others we can all learn from.

  If you have other mistakes you see the most, feel free to drop me a DM on LinkedIn.

  You can also check out my newsletter, High Growth Engineer, where I share how to grow faster as a software engineer to 50k+ engineers weekly.

  See you there!

  Read more

  Open in new tab

• Top Headless UI libraries for React in 2024

  Explore some of the best headless UI libraries for React in 2024.

  Level

  Starter

  Tags

  #react#css#resources

  ---

  Author

  Feilin Liangga Putri

  4 min read

  Feb 29, 2024

  Copy link

  Share

  ---

  

  Headless UI libraries are a modern trend in web development that focus on providing the underlying logic and functionality for UI components without prescribing a specific visual style. This approach allows developers to build fully accessible UI components according to their design systems without being tied to any predefined styles or aesthetics.

  Radix UI

  

  Radix UI, an open source component library, prioritizes fast development, easy maintenance, and accessibility. With 32 components available, it streamlines development by removing the need for configuration, allowing developers to quickly incorporate its components into their projects.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~13.5k
  • Npm weekly downloads: ~1,345,900
  • No. of components: 32

  Headless UI

  

  Next, Headless UI provides completely unstyled and fully accessible UI components.The diverse array of elements in Headless UI is meticulously crafted to function effectively within the system, making it an excellent option for individuals who prioritize developing custom, inclusive interface designs with a distinct visual aesthetic.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~23.6k
  • Npm weekly downloads: ~1,300,810
  • No. of components: 10

  React Aria

  

  React Aria is a library of React Hooks that provides accessible UI primitives for your design system. There are over 40 components with built-in behavior, adaptive interactions, accessibility, and internationalization, ready for your custom styles. It provides an excellent user experience, notably with functions such as screen reader assistance, keyboard controls, focus handling, language translations, and additional features.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~11.1k
  • Npm weekly downloads: ~116,538
  • No. of components: 35

  Aria Kit

  

  In addition, Aria Kit is an open-source library that provides unstyled, primitive components for building accessible web apps, design systems, and component libraries with React. It contains a collection of components that handle accessibility, state management, and keyboard interactions, while leaving the styling and composition to the user.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~7.5k
  • Npm weekly downloads: ~53,787
  • No. of components: 25

  Ark UI

  

  Ark UI is a headless library known for building reusable, scalable design systems that works for a wide range of JS frameworks. The components are unstyled, declarative, accessible, and reliable, allowing for a delightful development experience. It supports multiple platforms and applications, helps create a consistent design system across them and uses state machines to ensure predictable and bug-free behavior in every component.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~2.8k
  • Npm weekly downloads: ~29,155
  • No. of components: 37

  Reach UI

  

  Furthermore, Reach UI is a collection of accessible, React-based UI components for building design systems. This prioritization of accessibility results in user-friendly components that enhance inclusivity in web applications. Reach UI's components adhere to accessibility best practices, simplifying the process for developers to build applications suitable for all users, including those who depend on assistive technologies.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~5.9k
  • Npm weekly downloads: ~42,685
  • No. of components: 15

  

  The headless UI library ecosystem for React showcases a vibrant collection of tools designed to meet a wide range of web development needs. From accessibility and ease of use to customization and scalability, each library offers distinct advantages, reflecting the industry's shift towards more adaptable and inclusive web design practices. As web development continues to advance, the flexibility and user-focused design of headless UI libraries will remain essential for shaping the future of digital interfaces.

  Read more

  Open in new tab

• Top Open Source Design Systems by Tech Companies You Can Use Right Away

  Explore some of the best open source design systems provided by tech companies.

  Level

  Starter

  Tags

  #resources

  ---

  Author

  Feilin Liangga Putri

  6 min read

  Feb 28, 2024

  Copy link

  Share

  ---

  

  Open source design systems by tech companies provide a wealth of knowledge and insights into best practices, innovative solutions, and collaborative processes between designers and developers. Here are some of our favorite by popular tech companies:

  Gestalt by Pinterest

  

  Gestalt by Pinterest is a design system designed to enhance UI consistency and quality. Its set of components and rules are tailored to fit Pinterest's specific look and how it works. It's also great at creating easy-to-use interfaces, paying special attention to making sure everyone can use them easily, no matter their abilities.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~4.2k

  Material Design by Google

  

  Material Design by Google is a system for design that helps in developing consistent, visually pleasing, and effective UI for various platforms and devices. It includes grid-based layouts, responsive animations, transitions, and many more. All these are made by using a minimalist design approach.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~8.2k

  Blueprint by Palantir

  

  Next, Blueprint by Palantir is a collection of reusable components, interactive documentation, and accessibility features for the web, built on React. Its emphasis on growing easily and being interactive makes it especially good for big company apps in fields that need to handle a lot of complex information.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~20.3k

  Polaris by Shopify

  

  Polaris, created by Shopify, is a design system that assures a consistent user experience on its platform. It has detailed guidelines on various components that follow Shopify's design standards. This allows for it to have easy-to-use and readily available shopping experiences for both sellers and buyers.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~5.6k

  Lightning by Salesforce

  

  Lightning by Salesforce provides ready-to-use HTML and CSS UI elements that can be used to develop Salesforce experiences. It explains the visual design values and attributes that ensure branding and UI consistency at scale.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~3.5k

  Primer by GitHub

  

  Primer by GitHub contains guidelines, principles, and patterns for designing UI at GitHub, with the aim of ensuring consistency and usability across GitHub's platforms. It includes design guidelines, components, and tools that reflect GitHub's specific needs for collaborative coding environments, which is particularly important to ensure clarity and efficiency in complex interfaces.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~2.9k

  Spectrum by Adobe

  

  Spectrum, Adobe's design system, is engineered to enhance user experience across its diverse platforms. By focusing on being flexible and creative, it can become really good at being easy to use and looking great, setting a high bar for how user interfaces should look.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~11.1k

  Carbon by IBM

  

  Carbon by IBM is an open source design system for products and digital experiences, based on the IBM Design Language. With its comprehensive set of design guidelines and development components, Carbon is designed to facilitate the creation of intuitive and efficient user interfaces, particularly for complex enterprise solutions requiring scalability and integration.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~7.4k

  Ring UI by JetBrains

  

  Ring UI by JetBrains is a collection of UI components for web-based products built inside JetBrains or third-party plugins for JetBrains’ products. It's designed to help developers build consistent, responsive, and attractive interfaces quickly. Ring UI emphasizes productivity and user experience, reflecting JetBrains' expertise in development tools.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~3.5k

  Base Web by Uber

  

  In addition, Base Web by Uber is a React component library that offers a robust suite of components out of the box. It offers an extreme level of customization through the Overrides API and configurable Themes. Its scalability and wide-ranging component library make it appropriate for various web applications, such as large-scale enterprise systems or basic web projects.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~8.6k

  Atlassian Design System

  

  Atlassian Design System offers direction, elements, and materials for creating interfaces that match Atlassian's products like Jira and Confluence. It highlights teamwork, variation, and a unique visual design to support Atlassian's dedication to team productivity software.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: -

  Backpack by Skyscanner

  

  Backpack by Skyscanner consists of design tools, components, and guidelines that focus on providing a positive user experience on the Skyscanner website. Promoting modularity, scalability, and accessibility helps designers and developers quickly develop cohesive and user-friendly interfaces.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: 480

  Fluent by Microsoft

  

  Fluent by Microsoft is a collection of UX frameworks designed for developing web and mobile applications with the same appearance and function as Microsoft products.It emphasizes on motion and material-inspired interfaces for smooth and intuitive user experiences on Microsoft platforms and devices.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~17.4k

  Protocol by Mozilla

  

  Finally, Protocol by Mozilla is a design system for Mozilla and Firefox websites that provides a common design language, reusable code components, and high level guidelines for content and accessibility. It prioritizes web standards and open-source principles, making it a versatile choice for web projects aiming for clarity and user-friendliness.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: 251

  ---

  

  Design systems from top tech companies that everyone can use are a huge help for both designers and developers. They help make digital interfaces consistent, easy to use, and innovative. Each system has its own special features and ideas, showing how varied and vibrant the tech world is today.

  Read more

  Open in new tab

• Most Useful and Impactful React Ecosystem Libraries

  Explore some of the most useful and impactful React ecosystem libraries.

  Level

  Starter

  Tags

  #react#resources

  ---

  Author

  Feilin Liangga Putri

  5 min read

  Feb 27, 2024

  Copy link

  Share

  ---

  

  One of the best things about React is the rich ecosystem of libraries and tools that helps developers build apps quickly. Here, we list some enduring and widely favored React ecosystem libraries.

  Next.js

  

  Next.js, a full-stack React framework, is utilized by some of the biggest companies globally to build top-notch web applications. It offers automatic optimizations, data fetching, routing, server functions, API endpoints, and more, solidifying its position as a robust full-stack React framework.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~119k

  Remix

  

  Remix is a full stack React framework with a focus on web fundamentals and modern web app UX, enabling developers to build better websites with faster and smoother user experiences. It allows data loading, code splitting, and UI transitions to be handled by the URL segments, resulting in snappy page loads and instant transitions. Furthermore, it supports HTML forms, handles both the server and client side, has built-in error handling, and supports route error boundaries. Its abundance of features allow it to stand-out as one of the most impactful React libraries.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~26.7k

  React Query

  

  Additionally, React Query is a library that provides declarative, always-up-to-date auto-managed queries and mutations for data fetching in React applications. It handles caching, background updates, stale data, and many more with zero-configuration. It simplifies data fetching logic, improves developer and user experiences, supports complex workflows, and works with any backend.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~38.7k

  Docusaurus

  

  Docusaurus is a react-based static website generator. It includes customization, localization, versioning, search, and dark mode features to improve user experience and aid in documentation creation.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~51.5k

  React Hook Form

  

  React Hook Form allows for better form state management and validation as it is a library for building forms in React with less code and better performance. It offers a feature-complete API, a constraint-based validation system, a small package size, minimal re-renders, easy adoption, and consistent validation strategies.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~38.9k

  React Router

  

  React Router is instrumental in implementing declarative routing within React applications. Its approach simplifies the creation of dynamic, single-page applications, allowing developers to manage navigation and view transitions with ease. The library's popularity and utility in the React ecosystem are evident from its GitHub stars, underscoring its role in shaping modern web application development.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~51.7k

  Redux / React Redux

  

  Redux / React Redux is a predictable state management for JavaScript apps in a consistent, predictable, and testable way. It enables powerful features like undo/redo, state persistence, and more. One of its features, Redux DevTools, can debug and trace state changes, with time-travel and error reporting capabilities. Most importantly, Redux works with any UI layer and has a large ecosystem of addons to fit different needs.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~60.3k

  Framer Motion

  

  Meanwhile, Framer Motion is an open source, production-ready animation and gesture library for React on the web. Possessing straightforward syntax, robust capabilities, and optimized performance make it one of the most valuable libraries in the React ecosystem.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~21.4k

  React Testing Library

  

  React Testing Library is one of the best choices for testing React components that emphasizes user experience, providing easy-to-use APIs for different frameworks such as Angular, Vue, and React. It also includes extensions for Cypress and React Native, which further displays its versatility and effectiveness.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~18.5k

  React Email

  

  React Email consists of high-quality, unstyled components for creating beautiful emails using React. The components are responsive, accessible, customizable, and compatible with most email clients. They also back server-side rendering and CSS inclining, making it a valuable tool in the React ecosystem for creating impactful email campaigns.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~11.7k

  React Use

  Last but not least, React Use is a large library of React hooks, ported from libreact, that provide various functionalities for React components. This shows how it can be a valuable resource for developers seeking to enhance their applications with custom hooks, as reflected in its GitHub stars.

  By the numbers (accurate as of 26th Feb 2024):

  • GitHub stars: ~39.8k

  

  The React ecosystem consists of countless libraries that streamline web development and tackle many different challenges. Each of the libraries mentioned have a crucial role in improving the quality and efficiency of web apps development. With strong community support, the React ecosystem is a dynamic and invaluable resource for developers.

  Read more

  Open in new tab

• Top React UI Component Libraries in 2024

  Explore some of the most popular React UI component libraries.

  Level

  Starter

  Tags

  #react#resources

  ---

  Author

  Feilin Liangga Putri

  4 min read

  Feb 26, 2024

  Copy link

  Share

  ---

  

  UI component libraries improve developer efficiency by enabling consistent design and code reuse. As the top JavaScript frameworks, React offers a wide range of UI component libraries. This article will delve into some of the most popular and robust options available.

  MUI (formerly Material UI)

  

  MUI, previously known as Material UI, provides React developers with a range of free UI tools including a diverse component library, customizable themes, and production-ready components, all in line with Google's Material Design principles. This makes it an excellent option for creating visually appealing and powerful web applications.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~90.8k
  • Npm downloads (weekly): ~2,900,000

  Ant Design

  

  Ant Design uses CSS-in-JS technology to provide dynamic and mixed theme ability, and also improves the performance of the application by using component level CSS-in-JS solution. It is commonly used in the development of complex and large scale enterprise applications.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~89.4k
  • Npm downloads (weekly): ~1,100,000

  Shadcn UI

  

  Shadcn UI consists of beautifully designed components built using Radix UI and Tailwind CSS, which are accessible, customizable, and open source. They cover a wide variety of use cases such as dashboard, tasks, forms, music, and authentication.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~49.2k
  • Npm downloads (weekly): -

  Chakra UI

  

  Next, Chakra UI is a simple, modular and accessible component library for building React applications. It offers accessible, themeable, composable and light/dark UI components, as well as developer experience and community support, making it an excellent choice for developers who prioritize inclusivity and flexibility in their web applications. Its emphasis on composition and ease of styling allows for rapid development of attractive and accessible web interfaces.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~36k
  • Npm downloads (weekly): ~457,000

  Mantine

  

  Mantine is a React components library that offers more than 100 customizable components and 50 hooks for building accessible web applications faster. It supports visual customizations with props, styles overriding, and flexible theming with colors, fonts, shadows, and more – providing developers with a versatile toolkit for building responsive and visually appealing web applications.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~23.5k
  • Npm downloads (weekly): ~257,000

  React Bootstrap

  

  Additionally, React Bootstrap is a library that replaces the Bootstrap JavaScript with React components, without unneeded dependencies like jQuery. As one of the original React libraries, React-Bootstrap has grown alongside React, making it a great option.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~22.1k
  • Npm downloads (weekly): ~1,318,000

  Next UI

  

  Next UI is a beautiful, fast and modern React UI library that provides a plugin to customize default themes, a fully-typed API, and accessibility support. Its focus on design and user experience, along with a developer-friendly attitude, makes it a top pick for web developers.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~18.4k
  • Npm downloads (weekly): ~57,000

  Semantic UI

  

  Semantic UI is the official React integration for Semantic UI, a development framework that helps create beautiful, responsive layouts using human-friendly HTML. Semantic UI React is jQuery free, declarative, and has a rich set of components and subcomponents. It also supports augmentation, shorthand props, and auto controlled state.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~13.2k
  • Npm downloads (weekly): ~217,000

  PrimeReact

  

  Last but not least, PrimeReact includes advanced components like Data Tables, Trees, and more – offering a vast collection of widgets to build rich user interfaces. Its emphasis on theme customization and a wide array of components makes it suitable for applications demanding a high level of visual customization and functionality.

  By the numbers (accurate as of 22nd Feb 2024):

  • GitHub stars: ~5.3k
  • Npm downloads (weekly): ~104,000

  

  React UI component libraries in 2024 offer a variety of choices to meet different development needs and design preferences. These libraries cater to visual appeal, performance, and inclusivity. Their popularity, shown by GitHub stars and npm downloads, highlights their importance in the React ecosystem. As web development trends rapidly evolve, these libraries will likely continue evolving and taking an important part in web applications.

  Read more

  Open in new tab

• Best Large Open Source Next.js Projects to Study

  Understand how large scale web apps are structured by studying these Next.js projects.

  Level

  Starter

  Tags

  #react#nextjs#resources

  ---

  Author

  Feilin Liangga Putri

  6 min read

  Feb 19, 2024

  Copy link

  Share

  ---

  

  One of the most effective ways to grow as a developer is by studying real-world projects. In this article, we've curated a list of extensive Next.js projects for you to dive into and dissect. By exploring the architecture and codebase of these large-scale web applications, you'll gain invaluable insights into best practices, project structure, and advanced techniques.

  Whether you're a beginner looking to understand the fundamentals or an experienced developer aiming to refine your skills, these projects serve as valuable resources to elevate your proficiency and tackle complex challenges with confidence.

  Supabase

  

  Supabase is an open-source alternative to Firebase that offers a full PostgreSQL database, real-time functionality, simplified authentication, seamless storage integration, and additional features. It empowers developers to build scalable and secure web applications while maintaining compatibility with existing tools and extensions.

  Beyond the basics, Supabase offers additional features like embedding vectors (great for geospatial data), real time subscriptions, edge functions (serverless compute), migration guides, project management tools, a command-line interface (CLI), and integrations with other services.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~62.9k
  • Technologies: Tailwind, Radix, React Query, Valtio, Yup

  Cal.com

  

  Cal.com is an open-source scheduling tool that allows users to control their own data, workflow, and appearance. It is a successor of Calendly that is self-hosted or hosted by Cal.com, Inc. and can be deployed on the user's own domain.

  What's great about Cal.com is that it integrates with various services such as Google Calendar, Zoom, Daily.co, HubSpot, and more. It also supports customization, white-labeling, and API access. It has a built-in app store where users can add or remove integrations as they wish.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~27.2k
  • Technologies: Tailwind, React Hook Form, Radix, Zod, tRPC, Prisma

  Infisical

  

  Infisical is an open-source secret management platform that teams use to centralize their secrets like API keys, database credentials, and configurations. It offers a user-friendly dashboard, client SDKs, CLI, API, native integrations, Kubernetes operator, agent, self-hosting, secret versioning, role-based access controls, secret scanning, and more. The wide range of features offers ample opportunities for learning and experimentation within the Next.js ecosystem.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~11k
  • Technologies: Tailwind, Emotion, Radix UI, React Hook Form, Redux, React Query, Yup, Zod, Zustand, i18next

  Dub.co

  

  Dub.co is an open-source link management tool for modern marketing teams to create, share, and track short links. One most important feature is you can host Dub.co on your own server for more control over your data and design as an opportunity to experiment with Next.js.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~14.7k
  • Technologies: Tailwind, SWR, Prisma, PlanetScale

  Twenty

  

  Compared to alternatives, Twenty is great for the fact that it offers full control, freedom, and the ability to contribute, self-host, and fork, breaking away from vendor lock-in and allowing users to shape the open future of CRM. This is while also prioritizing data accessibility and visualization from various sources without retrofitting, and providing an effortlessly intuitive interface inspired by Notion.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~8.5k
  • Technologies: Chakra UI, React Hook Form, Zod, Apollo, GraphQL

  Inbox Zero

  

  Inbox Zero is an open-source email app that helps users reach inbox zero fast with AI assistance. Its unique feature is that it involves AI to help users manage their email subscriptions, automate their replies, block cold emails, and analyze their inbox.

  What's more, the AI lets users instruct the app in plain English to reply, forward, or archive emails based on certain rules. Users can also use planning mode to review the AI's suggestions before applying them.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~1.4k
  • Technologies: Tailwind, React Hook Form, Radix, SWR, Prisma, Zod

  Rallly

  

  Rallly is a web application that allows users to schedule group meetings with friends, colleagues and teams by creating meeting polls based on participants' availability. With the convenience of not having to sign up/login, users only have to simply enter their name and email to join a poll. Hence, this allows Rallly to have multiple advantages over alternatives, including its simplicity, privacy and customisation.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~2.8k
  • Technologies: Tailwind, Radix, React Hook Form, React Query, tRPC, Prisma

  Formbricks

  

  Formbricks is a free and open source survey platform that allows users to gather feedback from various channels and integrate with other tools. Users can create surveys with a no-code editor, launch and target surveys to specific user groups, invite team members to collaborate, and leverage Formbricks Insight Platform or build their own data analysis capabilities.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~5k
  • Technologies: Tailwind, Radix, React Hook Form

  Civitai

  

  Civitai is an open-source platform where people can share, collaborate, and learn from each other's stable diffusion models, which are techniques to customize AI generations. Users can also leave comments and feedback on each other's models to facilitate collaboration and knowledge sharing.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~5.2k
  • Technologies: Mantine, tRPC, Prisma

  Plane

  

  Plane is an open source project management tool that helps you track your issues, epics, and product roadmaps in the simplest way possible. As a platform used by over a thousand companies across countries, it offers a minimalist and intuitive interface, a powerful query language, a flexible workflow system, and integrations with popular tools like GitHub, Slack, and Figma.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: ~22.5k
  • Technologies: Tailwind, SWR, MobX

  Daily.dev

  

  Last but not least, Daily.dev is a professional network for developers to learn, collaborate, and grow together. Its feature involves customizing your feed, bookmarking articles, syncing across devices, and joining a community of developers.

  Its web app utilizes the brand new incremental static generation feature of Next.js to deliver pages fast, which makes it interesting to explore. This is used to deliver the latest programming news from top tech publications on any topic you want so that you can stay updated on the latest trends, learn new skills, and discover new opportunities in the tech industry.

  By the numbers (accurate as of 15th Feb 2024):

  • GitHub stars: 604
  • Technologies: Tailwind, React Query, GraphQL

  ---

  

  This collection of large-scale Next.js projects offers a rich learning environment for those seeking to deepen their understanding and hone their skills. By dissecting and exploring these real-world applications, we can gain valuable insights into advanced techniques, project structures, and best practices. Whether you're looking to master the fundamentals or refine your expertise, immersing yourself in these projects provides a hands-on opportunity to elevate your proficiency and tackle complex challenges with confidence. So, dive in, explore, and embark on a journey of continuous learning and growth within the Next.js ecosystem!

  Read more

  Open in new tab

• Core Web Vitals Metrics in 5 Minutes

  Understand how to quantify good user experience in web pages.

  Level

  Starter

  Tags

  #resources#performance

  ---

  Author

  Feilin Liangga Putri

  5 min read

  Feb 16, 2024

  Copy link

  Share

  ---

  

  As developers, we often wonder what kind of web page gives good user experience. The problem arises when we try to quantify it. Enter 'Core Web Vitals' – a set of key metrics provided by Google that constitute unified guidance for quality signals. It measures real-world user experience for loading performance, interactivity, and visual stability of the page.

  In this short article, we will summarize the most important things you should know about these metrics and provide you with links to learn more should you desire.

  Largest Contentful Paint

  

  The first metric to consider is the Largest Contentful Paint (LCP). LCP is a metric that measures the loading performance of a page. Specifically, it marks the point in the page load timeline from a user's perspective when the main/largest content (such as images or videos) has likely loaded.

  LCP is represented in seconds, where anything under 2.5 seconds is great. It is extremely crucial as it represents how quickly users can access the main content of a web page. The faster it is, the better user engagement, satisfaction, and retention. To monitor, platforms such as Google's PageSpeed Insights or Lighthouse can be used.

  LCP is affected by several factors: Server response times, network latency, render-blocking resources, and the complexity of the web page's layout. Optimizing these factors can help improve LCP and overall loading performance.

  Examples of such optimization techniques include:

  • Optimizing images and videos: Compressing images, using modern image formats, and lazy loading techniques
  • Minimizing render-blocking resources: Minimize synchronous stylesheets/scripts or long tasks
  • Prioritizing critical content: Preloading critical resources, optimizing server response times (reduce time to first byte), and prioritizing above-the-fold content
  • Implementing efficient caching: Leveraging browser caching, Content Delivery Networks (CDNs), and optimizing cache policies

  Useful links

  • Largest Contentful Paint (LCP) | web.dev
  • Optimize Largest Contentful Paint (LCP) | web.dev
  • Largest Contentful Paint (LCP): What It Is & How to Improve It

  First Input Delay

  

  First Input Delay (FID) is also an important metric that assesses the responsiveness of a web page. Different from LCP, FID evaluates the interactivity of a page by quantifying the time taken between users' first action (such as clicking a button or tapping on a link) and how long the browser takes to respond to that.

  A low FID (under 100 milliseconds) indicates that the page is highly interactive and responsive to user input, contributing to a positive user experience. Similar to LCP, FID is measured using performance monitoring tools like Google's PageSpeed Insights, Lighthouse, or web analytics platforms.

  As FID is affected by code execution time, main thread activity and the presence of long tasks that block the browser's responsiveness, the following methods will help in improving it:

  • Optimizing asset loading: Utilizing asynchronous loading for scripts, leveraging browser caching, and optimizing resource delivery
  • Prioritizing critical rendering path: Prioritizing above-the-fold content, optimizing server response times, and minimizing layout shifts
  • Avoid long tasks: Identify and optimize long tasks that monopolize the main thread by breaking up long tasks into smaller, more manageable chunks using techniques like code splitting, web workers, or offloading computation to background threads
  • Reduce third-party impact: Minimize the use of third-party scripts/services or implement lazy loading or asynchronous loading for non-essential third-party resources

  Useful links

  • First Input Delay (FID) | web.dev
  • Optimize First Input Delay (FID) | web.dev
  • First Input Delay (FID): A complete guide to optimizing FID

  Cumulative Layout Shift

  

  Lastly, Cumulative Layout Shift (CLS) measures visual stability by quantifying how much visible content moves around on the screen while loading and the total of all individual layout movement scores (ranging from 0 to 1) that happens while the page remains active. Layout shifts happen when visible elements on a page unexpectedly move to a different position, causing content to reorganize and disrupt user experience. A low CLS (under 0.1) means that the page's layout remains stable and consistent with minimum disruption for users.

  CLS is affected by the following factors:

  • Images without dimensions: Images that load without specified dimensions can cause layout shifts when they render and occupy space on the page
  • Ads and embedded content: Third-party ads, iframes, or dynamically loaded content can trigger layout shifts as they load and display on the page
  • Font loading: Changes in font size or style during page rendering can lead to text reflow and layout shifts
  • Dynamic content: Content that loads asynchronously or dynamically, such as user-generated content or live updates, can cause layout shifts as it appears on the page

  Hence, to reduce CLS, developers can try the following techniques:

  • Specifying image dimensions
  • Preloading and lazy loading
  • Reserving space for ads and embeds
  • Avoiding dynamically injected content

  Useful links

  • Cumulative Layout Shift | web.dev
  • Optimizing Cumulative Layout Shift (CLS) | web.dev
  • Cumulative Layout Shift (CLS): How (and Why) to measure it?

  ---

  

  Understanding and optimizing Core Web Vitals metrics are essential for developers looking to improve user experience and website performance. Multiple research shows that only about 40% of web pages pass these metrics. By focusing on them, developers can easily quantify the scores and performance of their web pages, giving users a great experience while visiting the website.

  Read more

  Open in new tab

• 10 Best Free Tailwind-based UI Component Libraries and UI Kits

  Build your next project quickly with these Tailwind-based UI libraries.

  Level

  Starter

  Tags

  #css#tailwind#resources

  ---

  Author

  Yangshun Tay

  7 min read

  Jan 19, 2024

  Copy link

  Share

  ---

  

  Tailwind CSS' "write only atomic classes in your HTML approach" has long been regarded as a controversial and radical approach to styling since its inception. Over the years, the industry has started to see its benefits and Tailwind has since gained immense popularity.

  In this article, we explore the diverse range of free UI components and libraries that leverage Tailwind CSS, empowering front end developers to build modern and aesthetically pleasing user interfaces without compromising on efficiency or flexibility.

  Whether you're a seasoned developer or just venturing into the realm of Tailwind-powered design, this article is your compass to discover the most valuable and freely available UI component libraries that can elevate your websites to new heights.

  Sailboat UI

  

  Sailboat UI is a modern UI component library specifically designed for Tailwind CSS. It offers over 150 open source components, and uses Alpine.js for some interactive components. However, the important part of the examples is the Tailwind classes used, so you can easily integrate it with your favorite headless UI library in a framework of your choice.

  What is great about Sailboat is that it offers a few variants of each component. For example, Accordions are offered in multiple styles like simple, bordered, with background, etc, so you can choose a variant that suits your theme and brand.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 28
  • Sections/blocks: N/A
  • GitHub stars: 1,076
  • Mode of usage: Copy/paste HTML and CSS
  • Framework integrations: Alpine.js

  HyperUI

  

  HyperUI is a collection of free copy-pastable Tailwind CSS components that has been around since 2021. It is very similar to Tailwind UI in that both contain components and sections for application, marketing, and e-commerce websites. Since it's pure copy pasting of HTML/CSS, there's nothing to install and you can integrate it with any headless UI library.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 27
  • Sections/blocks: 20
  • GitHub stars: 6,949
  • Mode of usage: Copy/paste HTML and CSS
  • Framework integrations: N/A

  Preline UI

  

  The most outstanding thing about Preline is its vast library of components and sections. At over 60 components and 170 sections, it is the largest free set of Tailwind component examples out there. The examples are all very well-built and look very polished. Last but not least, all the examples have full support for dark mode.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 60
  • Sections/blocks: 171
  • GitHub stars: 3,200
  • Mode of usage: Copy/paste HTML and CSS
  • Framework integrations: N/A

  daisyUI

  

  daisyUI is one of the first Tailwind-based UI component libraries in existence. The library takes a unique approach where it provides a Tailwind plugin that injects its own higher-level classes that are composed of Tailwind utility classes. This somewhat defeats the purpose of Tailwind's atomic classes approach as developers are using pre-built CSS classes, similar to Bootstrap. Nevertheless, with 28.5k stars, it's a wildly popular library that boasts a vast library of over 50 components with multiple variants and classes.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 56
  • Sections/blocks: N/A
  • GitHub stars: 28,494
  • Mode of usage: Import CSS from npm package
  • Framework integrations: N/A

  Tremor

  

  While many libraries are aimed at more general usage of marketing and e-commerce, Tremor is focused on dashboard and data visualization components. Beyond the standard UI components of accordion, button, forms, Tremor includes multiple visualization components – area chart, bar chart, donut chart, line chart, scatter chart, you name it, they have it.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 29
  • Sections/blocks: 5
  • GitHub stars: 14,227
  • Mode of usage: Import React components from npm package
  • Framework integrations: React

  NextUI

  

  Despite the name, NextUI has nothing to do with Next.js, the popular React metaframework. Since v2.0, Next UI is built on top of Tailwind CSS and React Aria and is one of the fastest growing UI libraries based on Tailwind. Like Tremor, to use Next UI, import React components from the npm package @nextui-org/react and use the components within your application.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 38
  • Sections/blocks: N/A
  • GitHub stars: 17,879
  • Mode of usage: Import React components from npm package
  • Framework integrations: React

  shadcn/ui

  

  If there was one library that took the world by storm in 2023, it'd be shadcn/ui, which is built on top of Tailwind CSS and Radix UI. While many other Tailwind UI libraries make developers copy the HTML/CSS or install the library as an npm dependency, shadcn takes an approach where you copy and paste any required component code into your projects; you have full ownership and control over the code. This approach has both merits and drawbacks. While you have full control over the components, the obvious downside is that you won't receive updates automatically and have to remember to sync any changes. This approach is best used by teams who have strong front end developers who have a need for customizing component appearance as well as the capability to maintain the components in the long term.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 46
  • Sections/blocks: N/A
  • GitHub stars: 44,449
  • Mode of usage: Copy/paste React components (manually or via CLI)
  • Framework integrations: React (but community forks available in Vue and Svelte)

  Park UI

  

  Park UI is a relatively new Tailwind library but is a strong contender to shadcn/ui. Park UI's usage approach is similar to shadcn/ui,

  Where shadcn/ui is coupled with Tailwind and Radix UI, Park UI is way more versatile. It has first class support for both Tailwind CSS and Panda CSS (another atomic CSS library that uses a JavaScript-first approach) and also integrates with React, Vue, and Solid via Ark UI, a headless UI library that has first party implementations with React, Vue, and Solid.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 40
  • Sections/blocks: N/A
  • GitHub stars: 842
  • Mode of usage: Copy/paste React components (manually or via CLI)
  • Framework integrations: React, Vue, Solid

  Pines UI

  

  Pines UI is a UI library built on top of Tailwind CSS and Alpine.js and offers multiple variants for each component. With black as its primary color, the default appearance of the components highly resemble shadcn/ui and Park UI.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: 26
  • Sections/blocks: 34 (more than a hundred available for Pro subscribers)
  • GitHub stars: 1,696
  • Mode of usage: Copy/paste components
  • Framework integrations: React

  Aceternity UI

  

  Last but not least, we have Aceternity UI. Built by the amazing Manu Arora, Aceternity UI is unlike the typical common UI component libraries introduced above. It is a collection of bespoke and carefully crafted UI sections built on top of Tailwind CSS and Framer Motion.

  Some of our favorite examples include the Hero Parallax, 3D Card Effect, and the Wavy Background. It's an extremely fast way to elevate your website's design and add a "wow" factor! We recommend using it along another UI component library of your choice.

  By the numbers (accurate as of 18th Jan 2024):

  • Components: N/A
  • Sections/blocks: 36
  • GitHub stars: Not open sourced
  • Mode of usage: Copy/paste components
  • Framework integrations: React

  

  Read more

  Open in new tab

• User Interface Components at Scale

  How thousands of engineers at big tech companies build user interface components.

  Level

  Advanced

  Tags

  #scalability#javascript#css

  ---

  Author

  Yangshun Tay

  4 min read

  Dec 23, 2023

  Copy link

  Share

  ---

  

  Now that we know how Meta writes JavaScript and CSS, let's see how they're used to build UI components.

  Standardize on a UI library/framework

  Naturally the company that created React will build all their applications using React. You won't find Angular, Vue, or Svelte in Meta's codebase and Meta is all-in on React. By focusing on a single UI framework, tooling, knowledge and expertise can be shared and transferred more easily. Moreover, any issues faced by Meta engineers can be solved in-house, by consulting the React team. Longer term larger issues can be addressed in React's roadmap.

  Component documentation

  To easily build and test React components, Meta engineers can write example files for these components to demonstrate how the component looks and behaves when using a certain combination of props, similar to stories in Storybook.

  All React components in the codebase that have example files are easily searchable within an internal tool and can be interacted with right within the browser. It is super handy for discovering common components and seeing how they are being used.

  Testing

  Unit testing of component interaction and behavior can be done using Jest and React Testing Library. Snapshot tests and screenshot tests can also be conveniently generated from the component examples.

  Headless components

  Each product Meta builds has its own design system with a React implementation of the UI components. Many UI components (e.g. buttons, dropdowns, modals, etc) have the same underlying logic, functionality, and accessibility features built in and that layer can be shared between UI components belonging to different design systems. Each design system only has to care about customizing the appearance. This shared logic and accessibility layer is known as headless UI components. Naturally, Meta has built its own headless components to be reused across product design systems.

  Companies looking to accelerate their UI components development should pick up one of the popular headless UI component libraries. For React, there's Radix UI, React Aria, and Aria Kit.

  Component analytics

  Meta also has internal tools to gain insights on how big a component's file size is (bytes) and analytics, e.g. which modules are depending on the component (importing the component) and how many times they are being used in the codebase. This is useful for tracking progress when deprecating components.

  Monorepo perils

  In a monorepo, it becomes too easy to import components from anywhere in the codebase. However, this is bad when a component is still under development and not ready to be used widely or when a component is meant to be deprecated. To prevent unwarranted usage of components, lint rules can be used to flag usages of the components outside of directories they are not allowed to be used in.

  Design-to-code

  An emerging technology trend / workflow is “Design to code”, meaning you turn designs from your designer into code that you can use directly within your app. Since Figma is the industry standard for designing digital products these days, a forward-looking styling approach will be one that's integrated with Figma and can support exporting of UI markup and styles from Figma designs. Companies like Builder.io and Locofy offer such solutions.

  Conclusion

  Over the years, new UI libraries offering different reactive approaches have emerged (e.g. Qwik and Solid). React may no longer be the most performant library, but in terms of the overall ecosystem, learning resources, financial backing, availability of developers proficient in it, React is still one of the safest choices. Moreover, React is still constantly innovating and improving, with projects like React Server Components and an optimizing compiler. However, it is more important to decide on a company-wide blessed framework that the team is comfortable with, than to choose the most trendy UI framework.

  For component examples and visual testing, Chromatic (by the maintainers of Storybook) and Percy are the leading choices available in the market.

  UI components scalability checklist

  • Company-wide recommendation for UI framework/library (e.g. React, Vue, Angular, Svelte)
  • Documentation of components
  • Testing of components (unit, screenshot, accessibility)
  • Use a headless UI component library
  • Component analytics
  • Design-to-code (optional)

  Read more

  Open in new tab

• CSS at Scale

  How thousands of engineers at big tech companies write CSS.

  Level

  Advanced

  Tags

  #scalability#css

  ---

  Author

  Yangshun Tay

  7 min read

  Dec 22, 2023

  Copy link

  Share

  ---

  

  Writing CSS at scale, particularly in large and complex projects, can present several challenges. Here are some common problems associated with scaling CSS:

  • Global namespace: CSS operates in a global scope, which can lead to naming collisions and unintended style overrides. As a project grows, managing the global namespace becomes increasingly challenging, and conflicts between styles become more likely.
  • Specificity issues: CSS specificity determines which styles apply to an element. As the project scales, managing and understanding specificity can become complex, leading to unexpected styling outcomes and difficulties in maintaining a consistent design.
  • Unclear dependencies: CSS classes can be created on the fly, and you can't be sure where a style is being used and whether it's still being used.
  • Huge stylesheets: When it is hard to determine whether certain styles are still being used, stylesheets become “add-only”. This leads to redundant or unused styles, as well as overly specific selectors, which contribute to larger file sizes and slower loading and rendering times.

  CSS approach

  CSS uses a global namespace, which causes many problems at scale when many developers are building into the same web application. Since the 2010s, Meta has been writing CSS using an approach called CSS modules, which solves some of the problems with CSS at scale – global namespace, including styles only on pages that use them, dead code elimination (only including the selectors that are still being referenced), and some others. Meta's CSS modules implementation is not open sourced but bundlers like webpack add support for something similar.

  In 2014, Christopher Chedeau gave an insightful talk about writing CSS within your JS. In 2018, Meta started their rewrite of facebook.com and announced a new way of writing CSS in JS, which is called StyleX. StyleX's API resembles CSS-in-JS libraries like Aphrodite and Glamor, and has these key features:

  • Generated atomic CSS stylesheet: An atomic CSS stylesheet has a logarithmic (flatter) growth curve because it's proportional to the number of unique style declarations rather than to the number of styles and features written. Hence the stylesheet does not grow as fast as the number of features and the file size will stay relatively similar even with thousands of features and pages. The cost is being paid by each page as the HTML size is now larger.
  • Type-safe: Property keys can be checked for typo mistakes as only a recognized set of keys are allowed (e.g. margin, padding, color, etc.). Components can decide which CSS properties they want to allow to be passed in as props (e.g. only margins allowed). This prevents users of your components from customizing in ways you don't want them to.
  • No runtime: The styles are extracted into a static CSS file at build time. Little/no JavaScript needs to be run to inject the styles. This is important to prevent Flash of Unstyled Content and instances where JavaScript is not executed or supported.
  • No specificity issues: Each atomic class declaration only contains one property and is not nested.
  • Determinism: With atomic classes, each class on a DOM element specifies a different underlying property, and you won't run into the issue of non-deterministic result which depends on the order of the classes in the stylesheet.

  The team responsible for rebuilding facebook.com gave a talk about StyleX during React Conf 2019 and also at React Finland. The process of open sourcing StyleX has been a long one and as of Nov 2023, StyleX is finally open sourced. A caveat about StyleX is that it needs extra configuration to work in UI frameworks that use custom file formats like Vue and Svelte.

  In the open source ecosystem, Tailwind CSS is the rage. Like StyleX, Tailwind also uses atomic CSS approach so they also share a similar benefit of a CSS stylesheet file that plateaus. However, since Tailwind CSS is just a set of atomic classes, you can use it within both JavaScript and HTML and even server-side Ruby templates. Out-of-the-box, the default Tailwind config provides a set of predefined classes (similar to design tokens) whereas StyleX does not.

  Panda CSS is a new atomic CSS-in-JS library by the creators of Chakra UI and it is the middleground of StyleX (library calls are compiled away, type-safe) and Tailwind (inline style declarations, provides some default styling tokens).

  The advent of React Server Components means that a whole category of styling libraries that relied on context for theming and runtime injection without any static stylesheet extraction will cease to work. Thankfully Tailwind and Panda CSS generate styles at build time and are fully-compatible with React Server Components.

  If you don't mind seeing multiple classes in your HTML or building only with HTML and CSS (or non-JavaScript templating approach), Tailwind CSS will be my recommendation. If you prefer a JavaScript-first approach for styling and type-safety is important to you, use Panda CSS. Panda CSS is similar to StyleX but has a larger community maintaining it.

  CSS preprocessing

  Just like how developers can use the latest language features of JavaScript by using Babel, developers can also use the latest CSS features by using a CSS preprocessor like PostCSS to automate routine CSS operations, utilize future CSS syntax, and enhance CSS's functionality.

  Using Tailwind and Panda removes the need for writing CSS directly, so you might not actually need to use PostCSS in your applications at all. By the way, Tailwind and Panda use PostCSS under-the-hood so you will still be using PostCSS, just not directly.

  Linting

  Because Meta uses StyleX for authoring styles, linting is done in JavaScript, which means ESLint and Flow. StyleX's type-safety features allow components to restrict styling props to be of only certain allowed properties (e.g. margin) and only allowed values (e.g. multiples of 4).

  Teams using Tailwind CSS should install the official Tailwind CSS Intellisense plugin which offers autocomplete, linting and previews for a class' underlying styles.

  If you're writing plain CSS or CSS modules, stylelint is the recommended linter.

  Design tokens

  Design tokens are essentially variables used to store design decisions such as colors, fonts, border radii, spacings, animations, and more. These tokens can be simple values like a number, color hex code, or more complex information like a typography scale (font size, line height, letter spacing).

  By using design tokens, teams can ensure consistency across their product. As the design system evolves, changes made to the tokens automatically propagate throughout the product, ensuring uniformity and reducing the risk of inconsistencies.

  On the web, design tokens can be implemented using CSS variables, or an object in JavaScript. Meta uses CSS variables for color tokens so that dark mode is essentially another set of color tokens. For spacing, border radii and other kinds of numerical values, tokens are not being exposed to developers because most design choices have been abstracted behind UI components built by the product's design system team.

  In my opinion, UI components don't capture every design requirement and it's useful to make design tokens available for product engineers to use. Your company's product design team would probably already have selected design tokens and used them in their design system.

  If you are using Tailwind or Panda CSS, the default configuration includes tokens for spacing, colors, typography, etc but they can be configured for custom design tokens. If you are not using Tailwind or Panda CSS and don't have a design system but want a similar default set of tokens, Open Props offers a good set of design tokens in the form of CSS variables.

  Conclusion

  An Atomic stylesheet is the recommended approach for styling on the web because the stylesheet size does not grow proportionately to the number of features/developers/products. Tailwind CSS and Panda CSS are modern libraries to achieve atomic stylesheet generation in a futureproof fashion that's compatible with React Server Components and a server-first component era.

  Styling scalability checklist

  • Use Atomic CSS to keep the stylesheet size small.
  • Use CSS preprocessors to enable the latest CSS language features.
  • Use CSS linters to standardize on practices.
  • Use standardized design tokens.

  Read more

  Open in new tab

• JavaScript at Scale

  How thousands of engineers at big tech companies write JavaScript.

  Level

  Advanced

  Tags

  #scalability#javascript

  ---

  Author

  Yangshun Tay

  9 min read

  Dec 21, 2023

  Copy link

  Share

  ---

  

  As web development continued to evolve, the demand for more advanced and modern features led to the development of ECMAScript 6 (ES6), also known as ECMAScript 2015. Released in June 2015, ES6 introduced a range of new features, including arrow functions, classes, template literals, and destructuring assignments, among others.

  Today, JavaScript is a ubiquitous language used not only for client-side web development but also for server-side development (Node.js) and mobile app development (React Native). The language continues to evolve, with ongoing efforts to enhance performance, introduce new features, and address the needs of modern web development.

  Use latest (stable) language features

  After the release of ES2015 / ES6, the ECMAScript specification transitioned to a yearly release cycle, allowing for a more agile development process and quicker incorporation of new features. Subsequent releases, such as ECMAScript 2016 (ES7), ECMAScript 2017 (ES8), and so on, brought additional improvements and features to the language.

  Using the latest JavaScript language features in web development is crucial for several reasons. First and foremost, it ensures compatibility with modern browsers and leverages performance improvements introduced in newer language versions. This not only enhances the user experience but also aligns development efforts with the evolving standards of the JavaScript ecosystem. Furthermore, modern features contribute to enhanced productivity, readability, and maintainability of code. Syntax improvements, abstractions, and functionalities like arrow functions, async/await, and class syntax make code more concise, organized, and easier to understand. By staying current, developers gain access to a broader ecosystem of APIs, libraries, and community support, fostering a better development experience and future-proofing their code. Keep your developers happy by enabling the latest technologies and language features.

  A combination of JavaScript compilers and polyfills allow developers to use the latest ECMAScript features. JavaScript compilers like Babel transpile newer language syntax into an older version while polyfills like core-js provide implementations for newer JavaScript APIs and they work together so that older browsers that do not support the features can still run the code. Google uses their homegrown Google Closure Compiler while Meta uses a combination of Babel and Flow.

  TypeScript, which offers type checking on top of enabling modern language features, is both a compiler and type checker, so you might not need Babel at all. Read on to find out more.

  Type-safety first

  Type-safety is extremely important in large companies and large codebase. Type-safety helps to eliminate an entire class of bugs during development that will not make it into production.

  Meta places such a high importance in type-safety that they have developed type-safe versions of / type checkers for every dynamic-typed language they use:

  • JavaScript: Flow
  • PHP: Hack
  • Python: Pyre

  Other big tech companies like Microsoft have developed TypeScript and Google has developed Dart, which further highlights the importance of using type-safe languages when developing at scale. These languages / type checkers are open sourced and available for all to use.

  Beyond catching and preventing type errors, type-safe languages are also easier to read and maintain. In VS Code, you can hover over a symbol to know its type. After all, code is read much more than it is written! The benefits of increased readability and clarity outweighs the learning curve in the long term. IDEs can also improve the developer experience by providing better autocompletion suggestions, and showing type errors inline.

  Although Flow is open sourced, the Flow team has publicly stated that open source support is not a priority. In the open source ecosystem, there are other alternatives for writing type-safe web applications like ReScript and Reason, which also have their roots in Meta, but they have lost traction in recent years.

  Automate via linters and formatters

  There are multiple ways to write and format code, and in a large codebase built by a large team, inconsistent coding styles across different files and developers make the code difficult to read and maintain. This lack of standardization can also hinder collaboration and slow down development, as more time is spent understanding and debugging the code instead of adding new features or improvements.

  Linting is the automated process of analyzing source code to detect errors, enforce coding conventions, and identify potential issues. Linters, or linting tools, play a crucial role in improving code quality by catching syntax errors, promoting consistent coding styles, and enforcing best practices. They contribute to error prevention, enhance code readability, and establish a uniform coding style across a project.

  Meta uses ESLint with eslint-plugin-flowtype for linting JavaScript. If you're using TypeScript, the recommendation would be ESLint with typescript-eslint. Configuring ESLint rules individually can be a chore, so it is recommended to use popular open source ESLint configs like eslint-config-airbnb as a starting point. Meta's internal ESLint config can be found at eslint-config-fbjs.

  It is recommended to add ESLint rules around sorting imports, sorting object keys alphabetically, sorting React component props alphabetically, etc. This reduces the chances of merge conflicts when developers edit the same file. Christoph Nakazawa, ex-manager on Meta's JavaScript infrastructure and React Native team published @nkzw/eslint-config which has a high degree of overlap with Meta's ESLint configuration.

  Coding style is another aspect that can be automated and benefits from consistency. Prettier is the de facto choice for formatting. In 2018, Christopher Chedeau ran a format-athon at Meta where he rallied around 20 engineers across the company to format the codebase with Prettier.

  Linting should ideally be executed during development so that errors and warnings are reflected within the IDE instantly. The fast feedback loop increases productivity as the developer can fix the issues on-the-spot while the context is still fresh. Autofix lint issues and format the code on save by adding to VS Code's settings.json:

  {
    "editor.formatOnSave": true,
    "editor.codeActionsOnSave": {
      "source.fixAll.eslint": true
    }
  }

  Runtime

  A JavaScript runtime is an environment where JavaScript code is executed. JavaScript was originally designed to be run in the browser, but these days JavaScript can also be run on the server using Node.js, which is the most popular server-side JavaScript runtime built on Google Chrome's V8 engine.

  Meta uses Hermes for server-side rendering of React, although Hermes was originally designed to run React Native apps on mobile platforms.

  There isn't much of a choice to debate about here. In the wild, most companies use Node.js and it has gotten really good in recent years. Deno and Bun are rising stars in the JavaScript runtime space and both offer TypeScript support out-of-the-box. Deno has a high focus on security by restricting access to sensitive runtime APIs by default, while Bun is extremely fast and includes a package manager, bundler, and test runner.

  Deno and Bun are still considered new so the risk is yours to bear if you decide to go with them.

  Officially-endorsed/supported libraries

  While the JavaScript language is rapidly evolving, in the last decade, there were huge gaps where the language left in terms of providing solutions to common product needs like functional utilities, datetime formatting and manipulation, etc. As a result, a rich ecosystem of utilities and libraries that cater to various development needs have emerged:

  • State management: Redux, Zustand, Jotai
  • Functional utilities: Lodash, Ramda, Underscore
  • Datetime: Moment.js, date-fns, Day.js
  • Internationalization: Format.js, i18next
  • Reactive programming: RxJS
  • Immutability: Immer, Immutable.js
  • Classnames: classnames, clsx

  Engineering leadership or a front end infrastructure team should make a decision on which libraries to use for various purposes. This prevents different libraries serving the same purpose being shipped in the same app and users end up paying the cost of downloading the JavaScript twice. Resources should also be committed to supporting internal developers facing issues with them and performing periodic codebase-wide upgrading of the library versions being used.

  Package management

  Finally, the last piece of JavaScript development to discuss is package management. Package management in JavaScript refers to the process of managing, distributing, and installing JavaScript libraries and tools within a project. A package manager is a tool that simplifies these tasks by automating the installation, versioning, and dependency resolution of external code packages.

  Back in 2016, Meta created Yarn as an improvement over npm, it introduced the concepts of lockfiles, fast installs, global offline caches, workspaces, etc. A key feature of a scalable package manager is locking down the version dependencies and an offline mirror. You don't want to be blocked from deployment if the npm registry goes down. At Meta, node_modules are installed via Yarn v1, scanned for vulnerabilities, and checked into the monorepo.

  These days, npm has mostly caught up with Yarn in terms of feature parity and Yarn has also undergone many changes since its initial launch. As of writing, Yarn is now v4, introduces Yarn Plug'n'Play, and is no longer maintained by Meta. Personally, my goto package manager these days is pnpm because it has the most features, has an amazing development experience, and is frequently updated.

  Conclusion

  TypeScript by Microsoft is now the de facto way to write type-safe web applications. Community support (learning resources, library type declarations) and developer tooling support (linters, IDE integration) for TypeScript is also extremely strong; new JavaScript runtimes like Deno and Bun also support TypeScript out-of-the-box. Even Google uses TypeScript as the primary language for Angular development, a UI framework created by them.

  You will benefit from choosing TypeScript, even if the size of your codebase is small.

  ---

  JavaScript scalability checklist

  

  • Use modern language features, syntax, and APIs.
  • Use a type-safe language like TypeScript.
  • Leverage linting and formatting to enforce coding style and educate best practices.
  • Officially-endorsed/supported libraries.
  • Use features or modern package managers, check in your node_modules / use an offline mirror.
  • Upgrade runtime and package versions periodically.

  Read more

  Open in new tab

• Web Apps at Scale – Introduction

  How thousands of engineers at big tech companies build web apps.

  Level

  Advanced

  Tags

  #scalability

  ---

  Author

  Yangshun Tay

  5 min read

  Dec 20, 2023

  Copy link

  Share

  ---

  

  Meta (previously Facebook) is known for its social media platforms and used by a huge number of users and services. Meta's websites include facebook.com, instagram.com, messenger.com, whatsapp.com, threads.net, meta.com, and more and are used by billions of global users monthly.

  Developing these websites consisting of thousands of pages by thousands of engineers is no simple feat. In this article, we will provide some insights of how big companies like Meta and Google handle front end development on such a large scale, the tools, methods, and strategies they use and how growing companies who face the same problems can adopt some of the approaches using alternatives in the open source ecosystem.

  Aside from Meta's huge web user base, Meta is also an interesting company to look at because between 2015 to 2020, Meta was the forerunner of modern front end development with the creation of popular open source front end technologies like React, React Native, Flux, Jest, GraphQL, Docusaurus, Relay, Draft.js, Yarn, and more. It's fair to say that Meta had a significant impact on the modern front end ecosystem.

  Disclaimer: I am no longer affiliated with Meta and this article does not represent Meta. Opinions and experiences are solely my own. I worked at Meta as a Front End Engineer from 2017 to early 2023 and things might have changed since then.

  Who am I?

  I am an ex-Meta Staff Engineer who led engineering teams to build meta.com and oculus.com. I was actively involved in the development of Meta's open source projects by creating Docusaurus 2, maintaining (and deprecating) Flux, and making small contributions to Lexical and Relay. Outside of front end development, I have also written multiple technical interview resources like Blind 75, Tech Interview Handbook, and Front End Interview Handbook, which have amassed over 100,000 GitHub stars.

  Overview of Front End at scale

  As a company grows, the number of features and number of engineers developing those features increase. Look at your company's front end code base and see:

  • How many different JavaScript or CSS frameworks are being used?
  • How many custom Button components have been built?
  • How big is your utils folder and how many duplicate utilities are present?
  • How many different React hook libraries are being used?

  If there are too many to count, congratulations, you have just identified tech debt. These problems start to occur because:

  • Existing solutions do not work for new problems.
  • No recommended practices or standardized ways for doing the same thing.
  • Different teams face similar problems.

  As a result of the above, teams solve the problems for themselves, because it's much faster to solve their own problem than to solve it for everyone. What can also happen is that someone tries to solve it for everyone, but the solution isn't sufficient and the next person comes along to “improve” the solution for their own use case without understanding the use cases of others and ends up making things worse for everyone, often in subtle unnoticeable ways like performance degradations.

  Duplicated code, different approaches to achieving a similar outcome, unusable existing solutions all contribute to tech debt. At scale and over a long period of time, tech debt that is seemingly small can compound and lead to disastrous business consequences like bugs, downtimes, and developer burn out. Thankfully, even small improvements will also lead to large benefits at scale when lots of products and people benefit from it.

  Metrics to measure

  Effective front end teams at scale score well on the following metrics:

  • Lead time for feature development: The amount of time it takes to develop a feature, get it reviewed, and ship it to production.
  • Deployment frequency: How often an organization successfully ships new releases to production.
  • Change failure rate: Percentage of changes that cause a bug/failure in production.
  • Product quality: Percentage of users having a good experience with the product. Does the website load fast enough? Does it mean the minimum accessibility standards? There are actually many ways to measure this, though they all have a varying level of subjectivity.

  ---

  Caveats

  

  It is important to know the nature of the organization you are in. Different types of organizations have different focuses and you should adapt your approach to the nature of the company and product. Tech debt and engineering scalability is not as important in certain companies for good reasons.

  Be also aware of premature optimizations. Sometimes what you think is a problem might just be a minor inconvenience that is not actually a critical problem to solve right now. Without thorough understanding of the problem, solving a problem prematurely and having to revert it later costs more time overall.

  As a Front End Engineer who mostly worked in product teams I'm not all that familiar with deployment infrastructure and the amazing product infrastructure work, so some parts will be glossed over.

  Read more

  Open in new tab

• 5 Most Important User Interface Questions to Master for Front End Interviews

  Practice these user interface questions if you are short on time to prepare for your front end interviews.

  Level

  Intermediate

  Tags

  #interviews

  ---

  Author

  Yangshun Tay

  7 min read

  Dec 19, 2023

  Copy link

  Share

  ---

  

  A common frustration when preparing for front end interviews is the sheer volume of questions to practice. There are over a 100 possible front end interview questions available on GreatFrontEnd. How do you choose the best questions to practice to get the highest return of investment on your time?

  Front end interview questions often revolve around a combination of fundamental JavaScript concepts, problem solving skills, layout building skills, and data structures and algorithms. To maximize your efficiency, we recommend practicing the most commonly-asked questions, along with those that touch multiple skills, so that you get all-rounded practice.

  In this list we will cover the most important User Interface questions to practice. Let's get started!

  Todo List

  Building a Todo list is a practical exercise that evaluates a front end engineer's ability to work with user interfaces, handle state, and perform basic CRUD (Create, Read, Update, Delete) operations. In the most basic form, candidates are asked to create a simple todo list where users can:

  1. Add new tasks to the list.
  2. Mark tasks as completed.
  3. Delete tasks from the list.

  It is a common interview question because it reflects real-world scenarios in front end development, where developers often create user interfaces to add new entries to a list, manipulate the list, and remove entries from the list.

  Building a well-implemented Todo list demonstrates proficiency in DOM manipulation, event handling, building accessible forms, event delegation, and state management. This is a question that can also have multiple potential follow-up questions:

  • Fetch suggestions from an API and display the suggestions in a combobox pattern.
  • Save the items to a persistent storage like localStorage or to a database and read from the storage.
  • Add undo/redo functionality.
  • Add reordering functionality.

  The ease of successfully implementing the follow-up questions is highly dependent on the quality of the basic implementation, so it's important to get the basic implementation right.

  Practice implementing a Todo List on GreatFrontEnd

  Tabs

  Tabs are a common UI pattern in web development, making this question practical and applicable to a front end engineer's daily tasks. Typically, candidates are asked to create a tabs UI component with the following requirements:

  1. Display three tabs: Tab 1, Tab 2, and Tab 3.
  2. When a tab is clicked, show the corresponding content for that tab and hide the content for other tabs.
  3. Apply a visual indication (e.g., styling change) to the active tab to show which tab is currently selected.

  For such questions, candidates might be asked to implement without using any external libraries or frameworks. Building a well-implemented Tabs component demonstrates proficiency in DOM manipulation, event handling, accessibility, event delegation, state management, and designing component abstractions. This is a question that can also have multiple potential follow-up questions:

  • Is the component well-encapsulated? Is it possible to have multiple Tabs components on the page each with its own state?
  • Add full keyboard support as per the WAI-ARIA Tabs pattern.
  • Add an API to dynamically add/remove tab items after the component has been initialized.
  • Load tab contents over an API.

  Practice implementing a Tabs component on GreatFrontEnd

  Tic-tac-toe

  A "Tic-tac-toe" front-end interview question typically involves creating a web-based version of the classic Tic-tac-toe game using HTML, CSS, and JavaScript. Typically, candidates are asked to create a tabs UI component with the following requirements:

  1. Display a 3 x 3 game board with cells that users can interact with.
  2. Allow two players to take turns placing their symbols (X and O) on the board.
  3. Determine and display the winner when a player forms a horizontal, vertical, or diagonal line of three of their symbols.
  4. Allow the option to reset the game for a new round.

  Implementing Tic-tac-toe assesses a candidate's understanding of DOM manipulation, event handling, building a grid-based layout, implementing non-trivial game logic, data structures and algorithms, and state management. Potential follow-up questions include:

  • Extending the game board to N x N with M consecutive symbols to win. A well-designed solution will make this easy.
  • Implementing undo/redo functionality.
  • Implementing an AI for a single-player mode.

  Practice implementing a Tic-tac-toe component on GreatFrontEnd

  Image Carousel

  An "Image Carousel" front end interview question typically involves creating a web-based image carousel or slider. The goal is to implement a user interface that allows users to view a sequence of images, navigate between them. More specifically:

  1. Display a series of images in a carousel format.
  2. Allow users to navigate between images using previous and next buttons.
  3. Include indicators (e.g., dots) to show the current position in the sequence.
  4. Implement a responsive design that works well on various screen sizes.

  For such questions, candidates might be asked to implement without using any external libraries or frameworks. Implementing an image carousel assesses a candidate's understanding of DOM manipulation, event handling, building a slider layout, CSS transitions, and more. There are many ways to implement an image carousel, each with its own pros and cons. Unsurprisingly, this question has tons of possible follow-up questions:

  • Adding animations or transitions to enhance the user experience.
  • Providing accessibility features like keyboard events, correct roles, states, and properties as per the WAI-ARIA Carousel pattern.
  • Loading images dynamically or from an external source.
  • Implementing additional features like autoplay, pause on hover, jumping to a specific image via an imperative API.

  Image carousel interview question, along with its follow-ups, can even evolve into a front end system design question as there are multiple performance optimizations to talk about, with image optimizations being key. It's a great front end interview question to practice.

  Read about how to design an Image Carousel on GreatFrontEnd

  Autocomplete

  An "Autocomplete" front end interview question typically involves creating an interactive autocomplete feature for a text input field. The goal is to implement a user interface that suggests and displays possible matches or completions as the user types into the input field.

  Here's a simplified example of an Autocomplete front end interview question has the following requirements:

  1. As the user types into the input field, use the input text to fetch and display matching suggestions.
  2. Display the suggestions in a dropdown or similar UI element below the input field.
  3. Allow the user to select a suggestion from the dropdown, updating the input field accordingly.
  4. Fetch suggestions asynchronously from a server (simulated with a mock API or using actual HTTP requests).

  Implementing an autocomplete assesses a candidate's understanding of DOM manipulation, event handling, asynchronous programming (fetching suggestions from a server), familiarity with CSS positioning, form handling, accessibility, performance, and the list goes on. It is the single most important question you can practice as it literally touches on every possible front end interview topic. Like the image carousel question, there are also many possible follow-up questions:

  • Debounce the API search.
  • Providing accessibility features like keyboard events, correct roles, states, and properties as per the WAI-ARIA Combobox pattern.
  • Caching results and showing results from cache.
  • Handling network race conditions.
  • ... and many many more.

  With the amount of things to talk about, this can also evolve into a front end system design question to have further discussions about what other APIs an autocomplete component can include, performance improvements, etc.

  Read about how to design an Autocomplete on GreatFrontEnd

  ---

  

  It goes without saying that there are more possible interview questions to practice, but many other interview questions build on top of the skills evaluated for the above questions. If you are short on time, practicing the above questions first will give your the highest return on investment and is highly recommended.

  All the best for your interviews!

  Read more

  Open in new tab

• 5 Most Important JavaScript Questions to Master for Front End Interviews

  Practice these JavaScript questions if you are short on time to prepare for your front end interviews.

  Level

  Intermediate

  Tags

  #interviews#javascript

  ---

  Author

  Yangshun Tay

  7 min read

  Dec 18, 2023

  Copy link

  Share

  ---

  

  A common frustration when preparing for front end interviews is the sheer volume of questions to practice. There are over a 100 possible front end interview questions available on GreatFrontEnd. How do you choose the best questions to practice to get the highest return of investment on your time?

  Front end interview questions often revolve around a combination of fundamental JavaScript concepts, problem solving skills, layout building skills, and data structures and algorithms. To maximize your efficiency, we recommend practicing the most commonly-asked questions, along with those that touch multiple skills, so that you get all-rounded practice.

  In this list we will cover the most important JavaScript questions to practice. Let's go!

  Debounce

  Debouncing is a crucial technique used to manage repetitive or frequent events, particularly in the context of user input, such as keyboard typing or resizing a browser window. The primary goal of debouncing is to improve performance and efficiency by reducing the number of times a particular function or event handler is triggered; the handler is only triggered when the input has stopped changing.

  import { debounce } from 'lodash';
  
  // Example usage for a search input field
  const searchInput = document.getElementById('search-input');
  
  const debouncedSearch = debounce(() => {
    // Perform the search operation here
    console.log('Searching for:', searchInput.value);
  }, 300);
  
  searchInput.addEventListener('input', debouncedSearch);

  In this example, the debounce function creates a wrapper function that delays the execution of the provided callback until a certain amount of time has passed since the last input event. This helps optimize performance by preventing unnecessary computations or network requests during rapid user input. Adjust the delay parameter based on the specific requirements of your application.

  Debounce is a frequently asked question in front end interviews, especially by big tech companies because it assesses the candidate's understanding of asynchronous programming, closures, and the this callback. The basic version of debounce isn't too hard to implement, so you might be asked to implement additional functionality that's available on Lodash's _.debounce:

  • Leading version: Invoking the callback at the start of the timeout instead of at the end.
  • Trailing version: Invoking the callback at the end of the timeout.
  • Maximum delay: The maximum time the callback is allowed to be delayed before it is invoked.

  Or you could also be asked to implement the Throttle function, which is the sister function of Debounce; it's important to understand the differences between them. Throttle is a common follow-up question to Debounce and vice versa.

  Practice implementing a Debounce function on GreatFrontEnd

  Promise.all()

  Promise.all() is an important feature in JavaScript for simplifying code needed to handle multiple asynchronous operations concurrently, especially if there are dependencies between them. It takes an array of promises and returns a new promise that resolves to an array of the results when all of the input promises have resolved, or rejects if any of the input promises reject.

  Proficiency with Promise.all() is an indicator of a front end engineer's ability to handle complex asynchronous workflows efficiently and manage errors effectively, making it highly relevant to their daily tasks.

  const promise1 = fetch('https://api.example.com/data/1');
  const promise2 = fetch('https://api.example.com/data/2');
  const promise3 = fetch('https://api.example.com/data/3');
  
  Promise.all([promise1, promise2, promise3])
    .then((responses) => {
      // This callback is only ran when all promises in the input array are resolved.
      console.log('All responses:', responses);
    })
    .catch((error) => {
      // Handle any errors from any promise
      console.error('Error:', error);
    });

  In this example, Promise.all() is used to fetch data from three different URLs concurrently, and the .then() block is executed only when all three promises have resolved. If any of the promises rejects, the .catch() block is triggered.

  It is a good question to practice for front end interviews because candidates are often evaluated on their mastery of asynchronous programming and whether they know how to implement polyfills. Promise.all() has many sister functions like Promise.race(), Promise.any(), which can also be asked in interviews, so you kill many birds with one stone by practicing Promise.all().

  Practice implementing Promise.all() on GreatFrontEnd

  Deep Clone

  In JavaScript, a deep clone function is used to create a new object or array that is entirely independent of the original object/array. This means that not only the top-level structure is cloned, but all nested objects and arrays within the original structure are also duplicated. In other words, changes made to the cloned object do not affect the original, and vice versa.

  // Original user.
  const user = {
    name: 'John',
    age: 42,
  };
  
  // Create a deep clone of the user.
  const clonedUser = deepClone(user);
  
  // Modify the cloned user without affecting the original.
  clonedUser.name = 'Jane';
  
  // Output the original and cloned user. The original is not affected.
  console.log('Original User Data:', user); // { name: 'John', age: 42 }
  console.log('Cloned User Data:', clonedUser); // { name: Jane', age: 42 }

  While not as frequently asked in interviews as some other questions, deep cloning showcases one's understanding of recursion and the various data types in JavaScript – how to recursively traverse an arbitrary object in JavaScript and process each encountered type.

  Practice implementing the Deep Clone function on GreatFrontEnd

  Event Emitter

  An Event Emitter class in JavaScript is a mechanism that allows objects to subscribe to and listen for events, and to emit events when certain actions or conditions occur. It facilitates the implementation of the observer pattern, where an object (the event emitter) maintains a list of dependents (observers) that are notified of changes or events. In fact, EventEmitter is part of Node.js' API.

  // Example usage
  const eventEmitter = new EventEmitter();
  
  // Subscribe to an event
  eventEmitter.on('customEvent', (data) => {
    console.log('Event emitted with data:', data);
  });
  
  // Emit the event
  eventEmitter.emit('customEvent', { message: 'Hello, world!' });

  Implementing an EventEmitter class involves knowledge of object-oriented programming, closures, this callback, and data structures and algorithms fundamentals. Possible follow-up questions include an alternative unsubscribing API.

  Practice implementing an Event Emitter on GreatFrontEnd

  Array.prototype.filter()

  Array.prototype.filter() is a built-in method in JavaScript that allows you to create a new array containing elements that satisfy a certain condition. It iterates over each element in the array and applies a callback function to determine whether the element should be included in the filtered array.

  // Example: Filtering out even numbers from an array
  const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  const oddNumbers = numbers.filter(function (number) {
    return number % 2 !== 0;
  });
  
  console.log(oddNumbers); // Output: [1, 3, 5, 7, 9]

  Array.prototype.filter() is commonly-asked questions in front end interviews by big tech companies, along with its sister functions, Array.prototype.map(), Array.prototype.reduce(), and Array.prototype.concat(). Modern front end development favors functional programming style APIs like Array.prototype.filter() and it is also an opportunity for candidates to demonstrate their knowledge of prototypes and polyfills. It seems easy on the surface, but there's much more to it:

  1. Are you aware of all the parameters accepted by the filter callback? Hint: there are 4!
  2. How does the filter callback handle sparse arrays?
  3. Does your implementation call the callback function with the right this value?
  4. What if the array contents is mutated by the callback function mid-traversal?

  Nailing these edge cases is paramount for acing front end interviews.

  Practice implementing the Array.prototype.filter() function on GreatFrontEnd

  ---

  If you're short on time, we recommend practicing these 5 questions, which takes around 3 hours.

  What do you think of these questions? Do you think there are other important questions to cover?

  Read more

  Open in new tab

• How to Evaluate Companies as a Front End Engineer

  Learn the key factors and essential questions that Front End Engineers should explore when evaluating companies.

  Level

  Starter

  Tags

  #career

  ---

  Author

  Yangshun Tay

  13 min read

  Dec 14, 2023

  Copy link

  Share

  ---

  

  Front End Engineering is a nuanced field within Software Engineering and not all companies place equal emphasis on nor have the need for. Choosing the right company is a pivotal decision that can shape the trajectory of a Front End Engineer's career.

  A careful evaluation of potential employers to ensure alignment with one's skills, aspirations, and work preferences. From the nature of business to technological stack to growth opportunities, the considerations are diverse and significant. In this post, we highlight key factors and essential questions that Front End Engineers should explore when evaluating companies. By delving into these factors, Front End Engineers can make informed decisions that not only resonate with their expertise but also contribute to a fulfilling and successful career.

  Here are some of the factors you should be considering when joining a company as a Front End Engineer:

  • Nature of business
  • Technology stack / Engineering practices
  • Organization structure
  • Leadership
  • Interview process
  • Compensation
  • Career progression
  • Talent pool
  • Open source & community contributions
  • Focus on design

  Let's dive into each factor.

  Nature of business

  How important is the front end web product to the success of the company? Is web the primary medium in which users consume the product or is web just used for internal dashboards?

  If front end web is important to the company, the company will likely want to hire the best front end engineering talent and compensate them well. As a Front End Engineer, it's also important to join such companies because if/when recession strikes, the less important departments will be the first to be let go. Ideally, you'd want to be in the important departments, be it recession or not.

  Web engineering is important to companies like Figma where the core product is within the browser or a native desktop app. On the other hand, web is not as important to a ridehailing company where users are using native mobile apps to book rides.

  What are the primary revenue streams for the business? What is the breakdown of revenue per platform?

  It goes without saying that companies will allocate more resources to revenue-generating platforms.

  Other questions to ask:

  1. Are there specific metrics used to measure the success of front end initiatives?
  2. Describe the unique business challenges the front end team faces within your industry?
  3. What is your target market and how do you plan to expand it? What devices do these markets use to consume the application/services?
  4. How do you see the industry evolving in the next few years, and where do you see the company within that context?

  Technology stack / Engineering practices

  What technology stack is the company on? Does the company bother to keep up with modern front end technologies or are the company's products still on jQuery and Bootstrap 3 with no intention to migrate?

  You don't want to be still working on legacy technologies and not improve your skills at your new job. A stack that includes modern front-end technologies can offer more relevant experience and contribute to your professional growth.

  Good companies should strive to keep their technologies updated as it improves the product quality and helps their employees stay relevant with industry needs.

  What are scalability and performance challenges the company has faced? Describe the technical challenges faced by the front end teams.

  If the technical challenges/bottlenecks are mainly on the back end, then back end is likely more important to the company than front end in the long run. Consequently, there will be more seniority composition of engineers will bias towards the back end and limited growth for front end engineers due to lack of complex front end work available.

  What is your approach to front end testing and quality assurance?

  If front end products are not tested thoroughly, the company is either small, or the front end products are not as important.

  Other questions to ask:

  1. Can you describe the current technology stack and why it was chosen?
  2. How does the technology stack support the company's goals and objectives?
  3. Are there any plans to adopt new technologies or tools in the near future?
  4. How do you handle technical debt and ensure the codebase remains maintainable?
  5. Can you discuss the deployment process and how frequently deployments occur?

  Organization structure

  How are engineering teams organized? Are there both front end engineers and back end engineers in the same team or are they in separate teams? How much back end engineering does a front end engineer have to do?

  Both ways of team organization can work, but you'd want to avoid a situation where you are the only front end engineer on a large team primarily made up of back end engineers where there are few senior to learn front end from. You might also be a victim of "bait and switch", where after you join a team, there isn't that much front end work to do and you end up spending most of your time doing back end work. That's not what you're hired to do in the first place, some might like it, but most don't.

  Is there a front end infrastructure team that takes care of common front end engineering needs across the company such as design system components, linting, build, performance, package upgrades, etc?

  If a medium/large-sized company does not have a dedicated front end infrastructure team, there is a good chance that the company does not have too many front end products to warrant the need for a front end infrastructure team. Another reason is that front end engineering quality is not important to the company.

  Other questions to ask:

  1. How are engineering teams organized within the company?
  2. Can you describe the reporting and collaboration structure for the front end team?
  3. What is the ratio of front end engineers to other engineering roles?
  4. How does the front end team collaborate with product managers and stakeholders?
  5. Are there cross-functional teams that include front end engineers, and how do they operate?
  6. What opportunities are there for front end engineers to lead projects or initiatives?
  7. How are front end tasks and projects prioritized within the organization?

  Leadership

  How much does leadership value front end engineering? How important is brand identity and design to the company?

  The former can be hard to find out as an outsider but you can roughly tell from the quality and aesthetics of the products. This is an important question to find out because leadership decides where to allocate resources to and the more important departments have a higher priority.

  What is the background of the leaders (especially the technical ones)?

  Leaders that were more product and design focused will tend to prioritize front end engineering quality.

  Other questions to ask:

  1. How involved is the leadership team in front end engineering decisions?
  2. What is the leadership's vision for the front end team's growth and development?
  3. How are successes and achievements within the front end team recognized by leadership?
  4. What qualities do you look for in leaders within the front end team?

  Interview process

  Is there a dedicated front end interview process or is the process the same as for general software engineers (back end heavy)?

  A dedicated front end interview process allows companies to assess candidates more thoroughly and accurately for front end engineering roles. It ensures that the evaluation is aligned with the specific skills and challenges associated with front end development, contributing to effective hiring decisions and the overall success of the engineering team.

  If there isn't a dedicated front end interview process, it could be a sign that leadership does not understand front end engineering well and there's no front end engineers in leadership roles. A front end interview process that does not test the right skills can result in non-optimal hires which brings down the company's quality of front end engineering.

  Other questions to ask:

  1. Can you describe the typical interview process for a front end engineer role?
  2. What kind of front end coding challenges or technical assessments can I expect?
  3. How do you evaluate front end skills such as HTML, CSS, JavaScript, and frameworks?
  4. Who will I be meeting with during the front end interview stages?

  Compensation

  Does the company pay front end engineers the same as back end / full stack / generalist software engineers?

  If a company pays different specializations of software engineering differently, it's an indication that some specializations are not as important as the rest, aka. Second class citizens. Many companies like Meta and Google pay Front End Engineers as much as Software Engineers. Don't settle for less.

  Even if companies pay the same salary for Front End Engineers, the offer salary shouldn't be the only factor you should consider. You should also consider the longer term aspects such as career progression, how feasible it is possible to grow to senior, staff levels and beyond.

  Career progression

  How does the career ladder for a front end engineer differ from a back end engineer? How high is the career ceiling for a front end engineer at the company? What level can you attain by focusing on front end development? What is the composition of backgrounds of the high-level engineers at the company?

  The career ladder for a front end engineer and a back end engineer can vary between companies, and the specific titles and levels may differ. The career ceiling for a front end engineer can be quite high in companies that have complex client products (e.g. Figma, Google Docs, VS Code, etc) or value the importance of user experience and interface design.

  In many other companies, the career ceiling for front end engineers is much lower. For such companies, front end engineers have to look beyond front end work and contribute strategically to the organization's goals in order to rise up the ranks.

  Companies which have high career ceilings for Front End Engineers (without them having to go into management) include Google, Meta, Microsoft, Airbnb, and Figma.

  As mentioned earlier, look out for where the technical challenges lie as the company grows. Complex front end technical challenges will warrant the need for senior and beyond front end engineers which is good for a career in front end engineering.

  Talent pool

  How many other front end engineers are there at the company? Who are the other front end engineers at the company? Are they experienced and people I can learn from to level up my front end engineering skills? Are the other front end engineers also passionate about modern front end technologies and frequently share knowledge with each other?

  Understanding the experience level of fellow front end engineers is crucial for evaluating potential learning and mentorship opportunities. Working alongside experienced peers facilitates skill development, as you can glean insights from their expertise and real-world projects.

  It's also important to know if there's a culture for sharing about modern front end technologies; A team that actively shares knowledge and embraces modern technologies suggests a dynamic and forward-thinking environment.

  Other questions to ask:

  1. How would you describe the current team of front end engineers at the company?
  2. What qualities do you look for when hiring new front end engineers?
  3. What is the seniority breakdown of front end engineers at the company?

  Open source & community contributions.

  Does the company have any open source projects? Does the company give back to open source by submitting upstream projects? Does the company have an engineering or design blog and their posts of high quality?

  Having a community presence contributes to the positive brand image of the company and demonstrates a commitment to transparency, collaboration, and giving back to the community. An engineering blog fosters a culture of knowledge sharing within the company and contributes to the professional development of team members.

  A company actively involved in open source contributions is likely to attract developers who are passionate about open source and community collaboration. It can be a deciding factor for top talent when choosing where to work.

  Being able to contribute to open source (be it the company's open source projects or projects used by the company)as part of your work helps to build up personal brand and credibility which is useful to show future employers.

  Other questions to ask:

  1. Does the company contribute to any open source projects related to front end development?
  2. Are software engineers encouraged to contribute to open source during work hours?
  3. Discuss any notable front end open source contributions made by the company or its employees?
  4. How does the company recognize and reward open source contributions from engineers?

  Focus on design

  Are the company's products visually appealing? Is there a cohesive brand identity and product interface? Do the products look like they are part of a design system?

  While Front End Engineers don't necessarily have to design, they have to work closely with designers and implement what the designers come up with. A design system provides a structured approach to design and development, promoting consistency, efficiency, and collaboration across teams. It is an essential tool for creating and maintaining a unified and user-friendly interface in software products. Building products without a proper design system will lead to inefficiencies and inconsistencies down the road. A lack of a proper design system or design department could also be an indication that design and front end engineering is not valued by the company.

  Other questions to ask:

  1. How is design and brand aligned across the products on the different platforms?
  2. Is there a brand / design system team in-charge of the company's brand and design system?
  3. Describe the relationship between the front end engineering and design teams?
  4. How does the company ensure a consistent design language across all front end projects?
  5. What design tools and methodologies do front end engineers use?
  6. How do the company measure the success of the front end design efforts?

  ---

  Evaluating a company holistically, from its tech stack to its commitment to innovation and the quality of its team, empowers you to make informed choices that align with your professional aspirations.

  By considering the factors outlined in this guide, you pave the way for a rewarding and fulfilling career, where your skills thrive, and your contributions leave a lasting impact on the digital experiences you help create.

  You are not just choosing a workplace; you are selecting a path that leads to your own advancement, innovation, and success as a Front End Engineer.

  Read more

  Open in new tab

• Best Medium-size Companies for a Fulfilling Front End Career

  Discover the best medium-sized tech companies for a great career as a Front End Engineer.

  Level

  Starter

  Tags

  #career

  ---

  Author

  Yangshun Tay

  9 min read

  Dec 12, 2023

  Copy link

  Share

  ---

  

  This is part 2 of our top companies series where we gathered the top tech companies for a fulfilling career as a Front End Engineer. Companies are selected based on the following criteria:

  • Nature and variety of web products
  • Complexity and quality of front end engineering
  • Contributions to open source ecosystem

  This post covers the list of the top medium-sized tech companies for front end engineers. For each company, we give a rating out of 5 on the following areas:

  • Projects: Diversity, complexity and uniqueness of the products.
  • Talent: Quality of talent.
  • Design: Emphasis the company places on design.
  • Compensation: How well compensated the employees are.
  • Outlook: The company's outlook.

  Airbnb

  Airbnb revolutionized the travel and hospitality industry with its online marketplace for lodging and experiences. The Airbnb platform is a prime example of good design meets good engineering with its user-friendly and aesthetically pleasing interface that is used globally and supports nearly 100 languages.

  Airbnb has made significant contributions to the open source community. Some of their notable open source projects include:

  • JavaScript Style Guide: A very popular style guide and ESLint config for JavaScript.
  • Enzyme: JavaScript testing utilities for React. It is no longer recommended since it relies on testing component implementation and the community has moved towards using React Testing Library.
  • Lottie: A library for rendering animations on the web and mobile.
  • visx: A collection of expressive, low-level visualization primitives for React.
  • Polyglot: A tiny i18n library.
  • React Dates: A datepicker library for React.
  • Hypernova: A service for server-side rendering your JavaScript views.

  Between 2015 to 2020, Airbnb is one of the most innovative companies in the front end space. Airbnb was one of the earliest companies to implement isomorphic/universal rendering on the web with the invention of Rendr, a library to render Backbone.js apps on the server. They also use server-driven UIs to dynamically build pages for web and mobile. Airbnb's front end team also spoke at React Conf 2019 about the process behind their design system.

  Noteworthy front end engineers from Airbnb include Harrison Shoff, known for his work on Airbnb's style guide and visx. Leland Richardson, Jordan Harband, Spike Brehm, Josh Perez, were previously from Airbnb and were instrumental in shaping Airbnb's strong front end engineering culture and establishing the company as a leader in the front end ecosystem.

  On the design front, Airbnb's Design department has a beautifully-designed blog and frequently shares their knowledge and resources with the designer community.

  Airbnb's front end interview process mostly focused on front end coding with just one round of algorithmic coding. However, Airbnb places a high emphasis on cultural fit as the full loop consists of two rounds of behavioral interviews where most companies only have one.

  As of writing, Airbnb has scaled back on their community contributions, possibly due to the global movement towards cost cutting. We no longer see as much front end innovation coming from Airbnb as compared to before. Some of Airbnb's famous libraries like Enzyme and React Dates have been moved out of the Airbnb GitHub organization and don't look maintained. Airbnb's design blog has been paused since 2022 and Airbnb's engineering and design social media accounts have been closed.

  It's important to note that at its core, the Airbnb platform is a CRUD application and the challenges lie in scaling the platform for new verticals; the products themselves are not technically sophisticated client applications like a collaborative editor or design tools. However, if you are a product engineer who enjoys translating beautiful designs into reality and bringing them into the hands of people globally, Airbnb is still a cool and great place to work.

  Rating: Projects (3/5), Talent (4/5), Design (5/5), Compensation (4/5), Outlook (3.5/5)

  Shopify

  A Canadian powerhouse, Shopify empowers businesses with its e-commerce platform, providing business owners with tools to create online stores. As these websites allow a high degree of customization by users while optimizing for performance and SEO, the Shopify platform requires complex, top quality front end engineering.

  Shopify is no stranger to open source and although most of their projects are targeting the Ruby ecosystem, there are a few notable front end projects from them:

  • Remix: Remix is a full stack web framework by the creators of React Routers that was acquired by Shopify and integrated into their products.
  • Polaris: Shopify's design system implemented in React.
  • Hydrogen: A set of opinionated components, utilities, and tools to build custom e-commerce storefronts powered by Remix and Shopify platform.
  • React Native Skia: High-performance React Native Graphics using Skia.
  • Draggable: A lightweight, responsive, modern drag & drop library.

  In recent years, Shopify hired many well-known developers from Google like Ilya Grigorik, Jason Miller (creator of Preact), Jake Archibald, and Surma. Ryan Florence and Michael Jackson of React Router fame ended up at Shopify thanks to the Remix acquisition.

  Shopify is an attractive workplace for front end engineers due to its innovative and varied product range, which offers opportunities for diverse and challenging work. The company is pushing the boundaries of e-commerce web development which demands cutting-edge development to enhance user experiences, providing developers a platform to work on impactful and widely-used applications. Shopify's embrace of the latest technologies and commitment to continuous improvement in the field also contribute to a dynamic and growth-oriented work environment. This, combined with a supportive culture and opportunities for professional development, makes Shopify a rewarding place for front end engineers.

  Rating: Projects (4/5), Talent (4/5), Design (4.5/5), Compensation (3.5/5), Outlook (4/5)

  Figma

  Figma has become a game-changer in the design software industry, offering a cloud-based interface design tool that enables collaborative work. Figma's apps (Figma and Figjam) are possibly some of the most complex applications to exist as it is extremely challenging to build a performant design tool in the browser that scales for large design files and also offers real-time collaboration.

  While Figma's direct contributions to open source are limited, its impact on the design and development community is substantial. Figma has won over the design market and has begun to focus their efforts on improving the design-to-code workflow with the introduction of Dev Mode and Storybook integration, making the product easier to use for developers.

  Figma’s focus on user interface and experience design aligns well with the core competencies of front end engineering. Furthermore, the company's innovative approach and commitment to cutting-edge technology provide a dynamic environment for professional growth and learning in the field of front end development. There's a good chance that engineers who work at Figma are passionate about design and creating great user experiences; it's always great to be surrounded by like-minded people.

  Rating: Projects (4/5), Talent (4.5/5), Design (5/5), Compensation (4/5), Outlook (4/5)

  Stripe

  Stripe provides payment processing solutions for e-commerce, characterized by their user-friendly and secure interfaces. Their front end work mainly involves creating straightforward yet secure checkouts and payment SDKs, dashboards for businesses to manage their account, prebuilt UI elements for developers who want to create their own checkout flows, and developer platform, which is a world-class example of great developer documentation.

  Stripe does not have too many contributions to open source but front end engineers at Stripe have been instrumental in advancing UI/UX in financial technology. Some of their projects include Markdoc, a powerful, flexible, Markdown-based authoring framework and Sorbet, a type checker for Ruby.

  Stripe is a great company for front end engineers and designers mainly due to its reputation for building elegant, user-friendly products. The company is at the forefront of financial technology, offering developers the chance to work on innovative, high-impact projects that shape the way businesses handle online transactions. Stripe's emphasis on clean, efficient code and cutting-edge technology aligns with the interests of developers who are keen on pushing the boundaries of web development. Additionally, Stripe's collaborative work culture and focus on professional growth make it a great environment for a front end engineering career.

  Rating: Projects (3.5/5), Talent (5/5), Design (5/5), Compensation (4.5/5), Outlook (4/5)

  Vercel

  Vercel is a cloud platform focused on enhancing the development and deployment experience for front end teams. Vercel's platform is designed to make building and deploying as straightforward as possible, emphasizing ease of use, universality, and accessibility. There's seamless integration with major JavaScript frameworks, like Next.js, Remix, Nuxt, etc so that deploying sites built using these frameworks becomes a breeze. On top of hosting, Vercel also provides logs, A/B testing, storage, analytics, performance tracking, and more.

  It's particularly known for creating Next.js, an open source web framework based on React. Next.js is currently the most popular meta framework for building React applications and innovating at breakneck speed especially after members of the React core team left Meta to join Vercel. Besides Next.js, Vercel is also behind projects like SWR, Turborepo, Turbopack, and SWC.

  The Vercel team can be said to be the Avengers of the web development ecosystem, a congregation of top front end engineering talents. Guillermo Rauch, CEO and founder of Vercel, is a well-known figure in the development community for his work on Next.js and Socket.io. Jared Palmer, a key figure in the JavaScript community joined Vercel after they acquired his startup Turborepo. Tobias Koppers, the creator of webpack, joined Vercel to work on the evolution of webpack, Turbopack. As mentioned above, some React core team members like Sebastian Markbåge, Andrew Clark, and Dominic Gannaway, joined Vercel to continue working on React and other projects. The list goes on.

  Vercel has taken Meta's place of being the industry leader in pushing the boundaries of front end innovation. Besides front end hosting, Vercel is also investing in AI with the creation of the Vercel AI SDK and v0, a tool for generative UI design.

  Rating: Projects (4.5/5), Talent (5/5), Design (4.5/5), Compensation (4.5/5), Outlook (4/5)

  Read more

  Open in new tab

• Best Big Companies for a Fulfilling Front End Career

  Discover the best big tech companies for a great career as a Front End Engineer.

  Level

  Starter

  Tags

  #career

  ---

  Author

  Yangshun Tay

  11 min read

  Dec 11, 2023

  Copy link

  Share

  ---

  

  When you're on the hunt for your next front end engineering role, it's not just about picking any company that'll have you. Companies differ in terms of domains, size, customers, etc. The importance of front end development to a company depends on the company's core offering. Naturally, a company that has a core product that is primarily used on the web will prioritize their front end engineering department, while for companies whose flagship products are mobile apps or hardware, front end development might take a backseat.

  Whether it's working on cutting-edge technologies, being surrounded by inspiring colleagues, or contributing to projects you're passionate about, the right company can elevate your career from ordinary to extraordinary. Choosing the right company can make all the difference between leading a fulfilling career and hitting arbitrary career ceilings.

  In this post, we have gathered the top tech companies for a fulfilling career as a Front End Engineer. Companies are selected based on the following criteria:

  • Nature and variety of web products
  • Complexity and quality of front end engineering
  • Contributions to open source ecosystem

  This post covers the list of the top big tech companies for front end engineers. For each company, we give a rating out of 5 on the following areas:

  • Projects: Diversity, complexity and uniqueness of the products.
  • Talent: Quality of talent.
  • Design: Emphasis the company places on design.
  • Compensation: How well compensated the employees are.
  • Outlook: The company's outlook.

  Meta (previously Facebook)

  Let's get the obvious company out of the way. Meta (previously Facebook), is a major player in social networking, digital marketing, and has recently ventured into the realm of augmented and virtual reality. The complexity of their front end work is showcased in the Facebook and Instagram platforms, which are known for their visually rich interface and smooth user experience. Unbeknownst to most, the most complex (and possibly most important) web application at Meta is their Ads Manager application as it has to display and manage thousands of rows of ad campaigns and also allow advertisers to create ad creatives in various formats for different platforms. The ads manager and business suite surfaces are worked on by thousands of engineers across the company.

  When the Facebook.com redesign was released in 2020, it was considered the gold standard for web applications as it popularized the concepts of SSR, lazy loading, prefetching on navigation, and data-driven dependencies. Today, most new applications at Meta are built using this JavaScript-centric tech stack.

  If I were to name a company that has the most impact on the open source front end ecosystem, it has to be Meta. Meta revolutionized how UI was built with the invention of React and React Native, introduced new data fetching approaches with GraphQL, built Jest, a feature-rich test runner that displaced then-frontrunner Mocha, made building documentation websites easy with Docusaurus, and Yarn, a package manager that was a huge improvement over npm at the time of its release. Meta has open sourced technology in almost every aspect of front end development most of which achieved widespread adoption at one point in time, which speaks volumes about the standard of Meta's front end engineers and importance of front end development to the company. Because much of Meta's front end technologies are open source and widely-adopted, new developers who had prior experience with these technologies will have an easier time when onboarding.

  Meta is continuing to lead innovation in the front end space with the development of React Server Components, Server actions, React forget, and cross-platform React components so that users can share components between web, mobile, and VR environments.

  Notable figures in front end development from Meta includes Jordan Walke, the creator of React and Reason; Joe Savona, who is currently working on the React Forget compiler; Dan Abramov, Sebastian Markbåge, Lauren Tan, Andrew Clark, Dominic Gannaway, Brian Vaughn, Sophie Alpert, Rick Hanlon, who have worked / are still working on React, Christopher Chedeau of Prettier and CSS-in-JS fame; and Christoph Nakazawa, who worked on React Native, Jest, and Metro.

  Meta's front end interview process is one that heavily favors Front End Engineers as it is focused on practical front end domain knowledge without excessive emphasis on algorithmic knowledge.

  While Meta is a great place for Front End Engineers, it can be stressful working there. The company is known for its fast-paced and results-driven work environment that rewards high performers, which can contribute to tight deadlines and stress. Employees may also face public scrutiny due to the company's high-profile nature and history with privacy concerns and misinformation. The demanding nature of the work and high expectations, coupled with potential challenges to work-life balance, are factors individuals should consider. On the engineering side of things, Meta is stuck using Flow for writing type-safe JavaScript, which is almost no longer used outside of Meta. However, there are some similarities with TypeScript, so the learning curve should not be too huge.

  Rating: Projects (4/5), Talent (5/5), Design (4/5), Compensation (4.5/5), Outlook (3/5)

  Google

  Google, a global technology leader, is best known for its search engine. However, the company's reach extends far into areas such as video streaming, cloud computing, AI, consumer hardware, and software solutions. Some of their products that showcase intricate front end development include YouTube, the world's top video streaming website; Google Maps, with its interactive maps and street views; Gmail, a widely-used email service featuring a sophisticated interface; and Google Docs, an online word processor offering real-time collaboration.

  Google's commitment to the front end open source ecosystem is evident in projects like:

  • Angular: One of the big three web application frameworks, popular among enterprise applications. The newly-released Angular 17 renews developers' confidence in the framework and that Google is still investing in it.
  • Chromium: The browser that powers Google Chrome. Did you know that other major browsers like Microsoft Edge, Opera, and Arc are also powered by Chromium?
  • Flutter: Google's approach of building cross-platform, natively compiled apps for mobile, web, and desktop from a single codebase. Dart is the primary language for developing Flutter apps.
  • Dart: A programming language by Google that can be transpiled to JavaScript but can also be used to build server, desktop, and mobile applications. Within Google, Dart is primarily used for building ads products.

  Google is home to many prominent figures in the front end community because they regularly create great guides and content for web development like web.dev and YouTube channels like Chrome for Developers. Paul Irish is known for his work on Chrome DevTools and other web development resources; Addy Osmani, Software Engineer on Google Chrome and author of numerous technical books; Minko Gechev, tech lead and manager for Angular.

  Google's front end interview process has a good balance of algorithmic knowledge and domain knowledge. There are pure algorithmic rounds and front end coding questions will also require a good grasp of software design and good data structure choice.

  Working at Google, while offering numerous benefits, comes with potential downsides. The large organizational structure of the company may pose challenges in communication and decision-making, and frequent reorganizations can create uncertainty for employees. Projects are often canceled and I have lost count of the number of instant messaging applications that were built, killed, and rebuilt. Despite these downsides, Google's cutting-edge projects, great salary, career growth opportunities, and focus on employee well-being continue to attract top talent.

  Rating: Projects (4.5/5), Talent (4.5/5), Design (4/5), Compensation (4/5), Outlook (4/5)

  Microsoft

  Microsoft, a household name in software, offers a range of products from operating systems to cloud services and business solutions. Besides Bing and Edge, the Microsoft 365 suite brings traditional workplace offerings like Word, Excel, and PowerPoint to the web which are complex web applications that require a high level of front end to create.

  For a long time, Microsoft was focused on desktop applications but in recent years, Microsoft has increased investment in developing the web ecosystem and have established themselves as one of the most important companies to the future of front end development with the following projects:

  • TypeScript: A popular type-safe superset of JavaScript. TypeScript mastery is considered a core skill these days.
  • Visual Studio Code: A free, highly customizable cross-platform code editor. It is one of the most popular IDE for web development and comes with out-of-the-box TypeScript integration.
  • Playwright: A framework for Web Testing and Automation. It allows testing Chromium, Firefox and WebKit with a single API.
  • npm: The de facto package manager for the JavaScript ecosystem is currently owned by GitHub, which is owned by Microsoft.

  Moreover, Microsoft is heavily investing in AI. They're the largest investors in OpenAI and OpenAI utilizes Azure as its primary cloud provider to train and run its large-scale AI models. Microsoft has been integrating OpenAI's technologies into its products, like GitHub Copilot, Microsoft 365 products and Bing search engine, among others. The partnership with OpenAI gives it a competitive edge in the AI race, especially against other tech giants like Google and Amazon. By closely working with and funding one of the most advanced AI research labs, Microsoft positions itself at the forefront of AI innovation.

  In a company as large as Microsoft, bureaucratic processes are often in place. This can mean slower decision making, more layers of management, and a need to navigate through a complex corporate structure to get things done. For some, this can feel restrictive and stifle creativity.

  Rating: Projects (4/5), Talent (4/5), Design (3.5/5), Compensation (3.5/5), Outlook (4/5)

  ByteDance/TikTok

  The only Chinese technology company on the list, ByteDance is most famous for its social media app TikTok, which is a highly addictive platform that prioritizes mobile-first short-form videos. While TikTok content is primarily consumed on mobile platforms, ByteDance has a large suite of enterprise offerings for the web, like Lark and BytePlus.

  ByteDance is actually pretty active in the open source community, though their projects are less known compared to those from Western big tech companies. One of ByteDance's most famous open source projects is rspack, a Rust port of webpack. Other notable projects include IconPark, a high quality, highly customizable icon set and Xigua player, a modern video player for the web.

  ByteDance is home to many talented individuals like Zack Jackson (Creator of module federation) and Dexter Yang (Author of Spellbook of Modern Webdev). Anthony Fu, one of the most prolific open source leaders in recent years, used to work at ByteDance.

  In terms of the hiring process, ByteDance's front end interview process is one of the toughest to crack due to their wide pool of questions that tests the candidates' breadth and depth in the domain. Candidates can expect to answer tough trivia questions about their favorite JavaScript framework and the front end domain. All of algorithms, JavaScript utilities, UI coding, and system design questions can also be asked.

  ByteDance is very similar to Meta in many ways and I often tell people they're the Meta of China – their focus on social products, performance-driven culture that disproportionately rewards high performers, mindset which encourages moving fast and taking ownership, open sourcing innovative technologies, etc.

  However, being a Chinese company, might have a corporate culture that differs significantly from Western norms. Engineers from different cultural backgrounds might find it challenging to adapt to these differences in work style, communication, and management practices. TikTok is constantly under scrutiny in the United States due to national security concerns related to its Chinese ownership and there's no knowing if or when the app will be banned in the US, which will hurt the business greatly.

  Rating: Projects (4/5), Talent (4/5), Design (4/5), Compensation (4/5), Outlook (4/5)

  Netflix

  Netflix, the leading entertainment streaming service, is renowned for its personalized user interfaces and seamless streaming experience across devices. Netflix is one of the best places for front end engineers not because of Netflix.com; it is their suite of complex web-based studio technologies that makes working there exciting.

  Netflix's primary contribution to the open source community is Falcor, a JavaScript library for efficient data fetching. Notable front end developers from Netflix include Jafar Husain, known for his work on reactive programming and JavaScript frameworks. Jafar has also worked at Meta on GraphQL.

  Netflix's company culture, often compared to a professional sports team, is centered around performance, collaboration, and a high degree of freedom and responsibility. This culture is detailed in their "Netflix Culture: Seeking Excellence" document and is widely recognized in the business world for its unique approach. Netflix is known for paying top of the market salaries for Software Engineers and mostly in base salary. Employees at Netflix have the flexibility to decide how much of their compensation is in cash or stock options. On the other hand, the dream team culture can lead to workplace competitiveness and increased stress as employees may feel they must constantly prove their worth to remain with the company.

  Rating: Projects (3.5/5), Talent (4/5), Design (4/5), Compensation (5/5), Outlook (4/5)

  Read more

  Open in new tab

• How to Handle Large Datasets in Frontend Applications

  Explore powerful techniques for handling large datasets in React application, including pagination, infinite scroll, and windowing

  Level

  Intermediate

  Tags

  #scalability#react#performance

  ---

  Author

  Nitesh Seram

  8 min read

  Jun 17, 2023

  Copy link

  Share

  ---

  

  Originally posted on https://niteshseram.in.

  Handling large datasets is a common challenge in frontend applications. As the amount of data grows, it can lead to performance issues, such as slow loading times and unresponsive user interfaces. In this blog, we will explore different methods to effectively handle large datasets in React applications. We will discuss techniques like pagination, infinite scroll, and windowing. By implementing these strategies, we can ensure that our frontend application remains fast and efficient, even when dealing with large amounts of data.

  Understanding the Performance Problems with Large Datasets

  Before we dive into the different methods of handling large datasets, let's first understand the performance problems associated with them. When an application tries to render or manipulate a large amount of data in a list, it can cause significant performance issues. This is because rendering a large number of DOM elements can be time-consuming and resource-intensive.

  To illustrate this, let's create a sample React application that renders a list of 10,000 records. By examining the performance of this sample application, we can better understand the challenges of handling large datasets.

  To get started, create a new React application using the create-react-app command in your terminal:

  npx create-react-app large-dataset-app

  Once installed, open the App.js file in the src directory and replace the existing code with the following:

  const data = new Array(10000).fill().map((_, index) => ({
    id: index,
    name: `Temp Name ${index}`,
    email: `Temp Email ${index}`,
  }));
  
  function App() {
    return (
      <div>
        {data.map((item) => (
          <div key={item.id}>
            <h3>{item.name}</h3>
            <p>{item.email}</p>
          </div>
        ))}
      </div>
    );
  }
  
  export default App;

  In this code, we generate an array of 10,000 objects, where each object represents a record in our dataset. We then use the map function to render each item in the array as a <div> element. Each <div> contains the name and email of the corresponding item.

  Now, start the React application by running the following command in your terminal:

  npm start

  Open your browser and navigate to http://localhost:3000. You will notice that it takes some time for the page to load, and scrolling through the list may also be slow. This is because rendering 10,000 DOM elements at once can cause performance issues.

  Pagination: Rendering Data in Pages

  One way to handle large datasets is by implementing pagination. Pagination allows you to render data in pages, rather than all at once. By controlling the amount of data shown on the page, you can reduce the stress on the DOM tree and improve performance.

  There are several UI libraries in React that provide pagination components, such as react-paginate. However, if you prefer not to use a UI library, you can implement pagination manually.

  To illustrate this, let's modify our sample application to include pagination. First, install the react-paginate library by running the following command:

  npm i react-paginate

  Next, open the App.js file and replace the existing code with the following:

  import { useState } from 'react';
  import ReactPaginate from 'react-paginate';
  
  const data = new Array(10000).fill().map((_, index) => ({
    id: index,
    name: `Temp Name ${index}`,
    email: `Temp Email ${index}`,
  }));
  
  function App() {
    const [currentPage, setCurrentPage] = useState(0);
    const itemsPerPage = 10;
    const pageCount = Math.ceil(data.length / itemsPerPage);
    const offset = currentPage * itemsPerPage;
    const currentData = data.slice(offset, offset + itemsPerPage);
  
    const handlePageChange = (selectedPage) => {
      setCurrentPage(selectedPage.selected);
    };
  
    return (
      <div>
        {currentData.map((item) => (
          <div key={item.id}>
            <h3>{item.name}</h3>
            <p>{item.email}</p>
          </div>
        ))}
        <ReactPaginate
          previousLabel={'Previous'}
          nextLabel={'Next'}
          breakLabel={'...'}
          pageCount={pageCount}
          marginPagesDisplayed={2}
          pageRangeDisplayed={5}
          onPageChange={handlePageChange}
          containerClassName={'pagination'}
          activeClassName={'active'}
        />
      </div>
    );
  }
  
  export default App;

  In this code, we use the useState hook to manage the current page state. We calculate the number of pages based on the total number of records and the desired number of items per page. We then use the slice method to get the current data to be displayed on the page.

  The ReactPaginate component renders a pagination UI with previous and next buttons, as well as page numbers. The onPageChange event handler updates the current page state when the user clicks on a page number.

  Now, when you run the application, you will see that the data is rendered in pages, with only a subset of records shown at a time. This helps to improve the performance of the application by reducing the number of rendered DOM elements.

  Infinite Scroll: Loading Data on Demand

  Another approach to handling large datasets is through the infinite scroll. Infinite scroll involves loading data incrementally as the user scrolls down the page. Initially, only a subset of data is loaded, and more data is appended as the user reaches the end of the list.

  There are various ways to implement infinite scroll in React, and one popular library for this purpose is react-infinite-scroll-component. To use this library, install it by running the following command:

  npm i react-infinite-scroll-component

  Next, open the App.js file and replace the existing code with the following:

  import { useState } from 'react';
  import InfiniteScroll from 'react-infinite-scroll-component';
  
  const data = new Array(10000).fill().map((_, index) => ({
    id: index,
    name: `Temp Name ${index}`,
    email: `Temp Email ${index}`,
  }));
  
  function App() {
    const [items, setItems] = useState(data.slice(0, 20));
  
    const fetchMoreData = () => {
      setTimeout(() => {
        setItems((prevItems) => [
          ...prevItems,
          ...data.slice(prevItems.length, prevItems.length + 20),
        ]);
      }, 1500);
    };
  
    return (
      <InfiniteScroll
        dataLength={items.length}
        next={fetchMoreData}
        hasMore={items.length < data.length}
        loader={<h4>Loading...</h4>}>
        {items.map((item) => (
          <div key={item.id}>
            <h3>{item.name}</h3>
            <p>{item.email}</p>
          </div>
        ))}
      </InfiniteScroll>
    );
  }
  
  export default App;

  In this code, we use the useState hook to manage the item's state. Initially, we load the first 20 items from our dataset. The fetchMoreData function is called when the user scrolls to the end of the list. It appends the next 20 items to the existing items using the spread operator.

  The InfiniteScroll component from react-infinite-scroll-component wraps the list of items. It takes the current length of the items as the dataLength prop, the fetchMoreData function as the next prop, and a boolean value to indicate whether there is more data to be loaded.

  When you run the application, you will notice that the data is loaded incrementally as you scroll down the page. This approach improves the user experience by providing a seamless scrolling experience while efficiently loading and rendering the data.

  Windowing: Efficiently Rendering Large Lists

  Another technique for handling large datasets is windowing. Windowing involves rendering only the visible portion of a list to the screen, rather than rendering all the items at once. This helps to reduce the number of DOM elements and improves performance.

  One popular library for windowing in React is react-window. It provides a set of components for efficiently rendering large lists. To use react-window, install it by running the following command:

  npm i react-window

  Next, open the App.js file and replace the existing code with the following:

  import { FixedSizeList as List } from 'react-window';
  
  const data = new Array(10000).fill().map((_, index) => ({
    id: index,
    name: `Temp Name ${index}`,
    email: `Temp Email ${index}`,
  }));
  
  const Row = ({ index, style }) => (
    <div style={style}>
      <h3>{data[index].name}</h3>
      <p>{data[index].email}</p>
    </div>
  );
  
  function App() {
    return (
      <List height={400} itemCount={data.length} itemSize={80} width={300}>
        {Row}
      </List>
    );
  }
  
  export default App;

  In this code, we define a Row component that renders each item in the list. The FixedSizeList component from react-window is used to render the list. It takes the height and width of the list, the total number of items, and the size of each item as props.

  When you run the application, you will see that only a portion of the list is rendered at a time, based on the height of the list. As you scroll through the list, the windowing technique efficiently renders only the visible items, resulting in improved performance.

  You might be wondering what’s the difference between what the react-infinite-scroll-component and react-window do. The difference is that in react-infinite-scroll-component load data incrementally as the user scrolls. It dynamically adds more items to the list as needed, creating an illusion of infinite content. react-window, on the other hand, renders only a subset of the list items that are currently visible in the viewport, reusing DOM elements as the user scrolls.

  Due to its simpler API and automatic handling of scrolling, react-infinite-scroll-component may be easier to set up and use for basic infinite scrolling needs. However, it may not perform as well with extremely large data sets or complex list items since it keeps all rendered elements in the DOM. In contrast, react-window's windowing technique ensures that only the visible items are rendered, resulting in improved performance and reduced memory footprint for large lists.

  Conclusion

  Handling large datasets in frontend applications can be challenging, but there are various techniques available to address this issue. By implementing pagination, infinite scroll, windowing, or using specialized libraries like react-virtualized or react-window, you can effectively manage large amounts of data while maintaining optimal performance.

  In this blog, we explored different methods of handling large datasets in React applications. We discussed pagination as a way to render data in pages, infinite scroll for loading data on demand, windowing for efficiently rendering large lists, and libraries like react-window that provide additional features for handling large datasets.

  Remember to consider the specific requirements and constraints of your application when choosing a method for handling large datasets. Each approach has its advantages and trade-offs, so it's important to evaluate which technique best suits your use case.

  By implementing these strategies, you can ensure that your frontend applications remain fast, responsive, and user-friendly, even when dealing with large amounts of data.

  Read more

  Open in new tab