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JavaScript Interview Questions

440+ most important JavaScript interview questions, from library APIs and utility functions to algorithms and UI components.
Solved by ex-interviewers
Test cases
Code in browser

Questions List

JavaScript Interview GuidesExplore our starter guides to get a solid grasp of JavaScript interview prep before jumping into practice.
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GUIDES
  • CounterWarm up questionBuild a simple counter that increments whenever a button is clicked
    Available frameworks
  • AccordionBuild an accordion component that a displays a list of vertically stacked sections with each containing a title and content snippet
    Available frameworks
  • Progress BarsBuild a list of progress bars that fill up gradually when they are added to the page
    Available frameworks
  • Mortgage CalculatorBuild a calculator that computes the monthly mortgage for a loan
    Available frameworks
  • TabsBuild a tabs component that displays a list of tab elements and one associated panel of content at a time
    Available frameworks
  • Data TableBuild a users data table with pagination features
    Available frameworks
  • Dice RollerBuild a dice roller app that simulates the results of rolling 6-sided dice
    Available frameworks
  • File ExplorerBuild a file explorer component to navigate files and directories in a tree-like hierarchical viewer
    Available frameworks
  • Like ButtonBuild a Like button that changes appearance based on the states
    Available frameworks
  • Modal DialogBuild a reusable modal dialog component that can be opened and closed
    Available frameworks
  • Star RatingBuild a star rating component that shows a row of star icons for users to select the number of filled stars corresponding to the rating
    Available frameworks
  • Todo ListBuild a Todo list that lets users add new tasks and delete existing tasks
    Available frameworks
  • Traffic LightBuild a traffic light where the lights switch from green to yellow to red after predetermined intervals and loop indefinitely
    Available frameworks
  • Digital ClockBuild a 7-segment digital clock that shows the current time
    Available frameworks
  • Tic-tac-toeBuild a tic-tac-toe game that is playable by two players
    Available frameworks
  • Image CarouselBuild an image carousel that displays a sequence of images
    Available frameworks
  • Job BoardBuild a job board that displays the latest job postings from Hacker News
    Available frameworks
  • StopwatchBuild a stopwatch widget that can measure how much time has passed
    Available frameworks
  • Transfer ListBuild a component that allows transferring of items between two lists
    Available frameworks
  • Nested CheckboxesBuild a nested checkboxes component with parent-child selection logic
    Available frameworks
  • Flight BookerPremiumBuild a component that books a flight for specified dates
    Available frameworks
  • Generate TablePremiumGenerate a table of numbers given the rows and columns
    Available frameworks
  • Progress BarPremiumBuild a progress bar component that shows the percentage completion of an operation
    Available frameworks
  • Temperature ConverterPremiumBuild a temperature converter widget that converts temperature values between Celsius and Fahrenheit
    Available frameworks
  • Accordion IIPremiumBuild an accessible accordion component that has the right ARIA roles, states, and properties
    Available frameworks
  • Accordion IIIPremiumBuild a fully accessible accordion component that has keyboard support according to ARIA specifications
    Available frameworks
  • Analog ClockPremiumBuild an analog clock where the hands update and move like a real clock
    Available frameworks
  • Data Table IIPremiumBuild a users data table with sorting features
    Available frameworks
  • File Explorer IIPremiumBuild a semi-accessible file explorer component that has the right ARIA roles, states, and properties
    Available frameworks
  • File Explorer IIIPremiumBuild a file explorer component using a flat DOM structure
    Available frameworks
  • Grid LightsPremiumBuild a grid of lights where the lights deactivate in the reverse order they were activated
    Available frameworks
  • Modal Dialog IIPremiumBuild a semi-accessible modal dialog component that has the right ARIA roles, states, and properties
    Available frameworks
  • Modal Dialog IIIPremiumBuild a moderately-accessible modal dialog component that supports common ways to close the dialog
    Available frameworks
  • Progress Bars IIPremiumBuild a list of progress bars that fill up gradually in sequence, one at a time
    Available frameworks
  • Tabs IIPremiumBuild a semi-accessible tabs component that has the right ARIA roles, states, and properties
    Available frameworks
  • Tabs IIIPremiumBuild a fully accessible tabs component that has keyboard support according to ARIA specifications
    Available frameworks
  • Progress Bars IIIPremiumBuild a list of progress bars that fill up gradually concurrently, up to a limit of 3
    Available frameworks
  • Birth Year HistogramPremiumBuild a widget that fetches birth year data from an API and plot it on a histogram
    Available frameworks
  • Connect FourPremiumBuild a game for two players who take turns to drop colored discs from the top into a vertically suspended board/grid
    Available frameworks
  • Image Carousel IIPremiumBuild an image carousel that smoothly transitions between images
    Available frameworks
  • Pixel ArtPremiumBuild a pixel art drawing tool where users can paint pixels with selected colors
    Available frameworks
  • Signup FormPremiumBuild a signup form that does validation on user details and submits to a back end API
    Available frameworks
  • Undoable CounterPremiumBuild a counter with a history of the values and ability to undo/redo actions
    Available frameworks
  • Users DatabasePremiumBuild a UI to filter, create, update, and delete users
    Available frameworks
  • Whack-A-MolePremiumBuild a popular arcade game where players attempt to hit moles as they pop up from holes in a board
    Available frameworks
  • Memory GamePremiumBuild a memory game where the player needs to match pairs of cards
    Available frameworks
  • Auth Code InputPremiumBuild an auth code input component that allows users to enter a 6-digit authorization code
    Available frameworks
  • Progress Bars IVPremiumBuild a list of progress bars that fill up gradually concurrently, up to a limit of 3 and allows for pausing and resuming
    Available frameworks
  • Data Table IIIPremiumBuild a generalized data table with pagination and sorting features
    Available frameworks
  • Modal Dialog IVPremiumBuild a fully-accessible modal dialog component that supports all required keyboard interactions
    Available frameworks
  • Data Table IVPremiumBuild a generalized data table with pagination, sorting and filtering features
    Available frameworks
  • Image Carousel IIIPremiumBuild an image carousel that smoothly transitions between images that has a minimal DOM footprint
    Available frameworks
  • Selectable CellsPremiumBuild an interface where users can drag to select multiple cells within a grid
    Available frameworks
  • Tic-tac-toe IIPremiumBuild an N x N tic-tac-toe game that requires M consecutive marks to win
    Available frameworks
  • Transfer List IIPremiumBuild a component that allows transferring of items between two lists, bulk selection/unselection of items, and adding of new items
    Available frameworks
  • WordlePremiumBuild Wordle, the word-guessing game that took the world by storm
    Available frameworks

JavaScript Interview Questions and Answers

Tired of sifting through poor-quality resources for JavaScript interview preparation? Our comprehensive collection of JavaScript interview questions and answers is your ultimate guide to mastering the skills you need for any JavaScript-based role.

Curated and answered by ex-FAANG interviewers with years of experience, our resource ensures you're prepared for a variety of challenges. Whether you're tackling algorithms, JavaScript functions, or building dynamic user interfaces, our questions are designed to reflect real-world scenarios. Each question is accompanied by detailed explanations, example solutions, and automated test cases, enabling you to refine your skills with immediate feedback.

Our resource is divided into two major categories: JavaScript Coding Interview Questions and JavaScript Quiz Interview Questions, covering a broad spectrum of topics essential for any JavaScript interview.

JavaScript Coding Interview Questions

Master critical JavaScript techniques and coding patterns with our curated list of JavaScript coding interview questions. These questions are designed to help you:

  1. Develop JavaScript data structures and algorithms: Solve challenges involving arrays, strings, linked lists, and more, sharpening your problem-solving skills with JavaScript.
  2. Create and optimize JavaScript Functions: Build modular, reusable, and efficient functions that form the backbone of scalable applications.
  3. Design user interfaces: Use JavaScript to manipulate the DOM, handle user interactions, and implement dynamic content.
  4. Handle real-world scenarios: Address challenges like API integrations, state management, and performance optimization.

Each coding question includes:

  • Example solutions: Step-by-step implementations written in JavaScript to guide you through the problem-solving process.
  • Automated test cases: Instantly validate your solutions, ensuring accuracy and correctness.
  • Best practices: Learn coding techniques that prioritize readability, maintainability, and performance.

Our in-browser coding workspace allows you to practice directly in your browser with no setup required. You'll gain hands-on experience with instant visual feedback, enhancing your understanding of JavaScript coding concepts.

Example coding questions you might encounter include:

  • How to implement a custom debounce function in JavaScript?
  • How to find the longest substring without repeating characters?
  • How to design a collapsible navigation menu dynamically?

Each challenge mimics real-world tasks, equipping you with practical skills that go beyond theory.

JavaScript Quiz Interview Questions

JavaScript quiz questions test your understanding of the language's fundamentals and intricacies. These trivia-style questions cover a wide range of topics, ensuring your readiness for interviews. Here's what you'll explore:

  1. Core JavaScript concepts: Understand key topics such as closures, scope, hoisting, and the event loop.
  2. Performance and optimization: Learn strategies for writing efficient JavaScript code and minimizing performance bottlenecks.
  3. Network and security: Gain insights into handling API requests, Cross-Origin Resource Sharing (CORS), and securing JavaScript applications.
  4. Testing and debugging: Familiarize yourself with tools and techniques for debugging JavaScript code and writing robust test cases.
  5. Advanced features: Explore concepts like async/await, Promises, and modern ES6+ features like destructuring, spread/rest operators, and modules.

Each quiz question comes with:

  • Concise answers (TL;DR): Clear and to-the-point solutions to help you respond confidently during interviews.
  • Comprehensive explanations: In-depth insights to ensure you fully understand the concepts and can elaborate when required.

Example quiz topics include:

  • How does the JavaScript event loop work?
  • What are the differences between let, const, and var?
  • How do you prevent memory leaks in JavaScript?

These questions ensure that you're not only familiar with JavaScript's syntax but also understand how to apply its features effectively in various scenarios.

Why Choose Our JavaScript Interview Questions?

  1. Credibility: All questions and answers are crafted by ex-FAANG interviewers with deep expertise in assessing candidates and building JavaScript solutions for large-scale applications.
  2. Comprehensive coverage: From algorithms and coding patterns to core concepts and advanced features, our resource spans every topic you need to master.
  3. Practical focus: Each question reflects real-world challenges, helping you develop skills that are directly applicable to your career.
  4. Interactive learning: Use our in-browser coding workspace to practice coding problems with instant feedback, simulating real interview conditions.

By leveraging this resource, you'll develop skills that go beyond typical interview preparation. You'll also gain confidence in tackling tasks like solving complex algorithms, debugging JavaScript code, and optimizing performance.

How These Questions Help You Excel

Our JavaScript interview questions are structured to help you:

  1. Master core JavaScript concepts: Strengthen your understanding of JavaScript's syntax, features, and best practices.
  2. Develop problem solving: Learn to approach challenges systematically, breaking them down into manageable steps.
  3. Gain hands-on practical experience: Practice coding problems and see your solutions come to life in our interactive workspace.
  4. Communicate effectively: Prepare to explain your thought process and solutions clearly, a crucial skill in technical interviews.

Real-World Applications

The scenarios covered in this resource aren't just theoretical. They reflect the types of challenges developers face daily, such as:

  • Designing efficient algorithms to process large datasets.
  • Writing reusable JavaScript functions for scalable applications.
  • Debugging and optimizing code for performance across various environments.

By mastering these areas, you'll not only be interview-ready but also prepared to excel on the job, making you a standout candidate for any JavaScript-related role.

Related lists

Check out other lists of questions below if you're looking for something more specific: