360+ JavaScript and TypeScript interview questions, from implementing common library APIs, utility functions, algorithms, to building UI components and more.
DebounceImplement a function to limit how many times a function can be executed by delaying the execution of the function until after a specified time after its last execution attempt
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Questions List
CounterWarm up questionBuild a simple counter that increments whenever a button is clicked
Available frameworks
Make CounterImplement a function that accepts an integer value and returns a function that can be repeatedly called to return increasing values
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MeanImplement a function that finds the mean of the values inside an array
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Min ByImplement a function that finds the minimum element based on the specified criteria
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StackImplement a stack data structure containing the common stack methods
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Type UtilitiesImplement utilities to determine primitive variable types in JavaScript
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CycleImplement a function that takes one or more values and returns a function that cycles through those values each time it is called
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Insertion SortImplement a function that performs an insertion sort
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Type Utilities IIImplement utilities to determine non-primitive variable types in JavaScript
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Mortgage CalculatorBuild a calculator that computes the monthly mortgage for a loan
Available frameworks
Binary SearchImplement a function that performs binary search on an array of numbers
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Breadth-first SearchImplement a breadth-first search algorithm that traverses a directed graph in a breadth-first manner
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Count ByImplement a function that counts the number of times a value appears in an array based on a function or property name
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DebounceImplement a function to limit how many times a function can be executed by delaying the execution of the function until after a specified time after its last execution attempt
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Depth-first SearchImplement a depth-first search algorithm that traverses a directed graph in a depth-first manner
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Heap SortImplement a function that performs a heap sort
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QueueImplement a queue data structure containing the common queue methods
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TabsBuild a tabs component that displays a list of tab elements and one associated panel of content at a time
Available frameworks
ClassnamesImplement a function that conditionally joins CSS class names together
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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
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Event EmitterImplement a class that can subscribe to and emit events that trigger attached callback functions
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File ExplorerBuild a file explorer component to navigate files and directories in a tree-like hierarchical viewer
Available frameworks
FlattenImplement a function that recursively flattens an array into a single level deep
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Merge SortImplement a function that performs a recursive merge sort
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Modal DialogBuild a reusable modal dialog component that can be opened and closed
Available frameworks
Promise.allImplement the Promise.all() function that resolves to an array of results if all the input elements are resolved or rejects otherwise
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Quick SortImplement a function that performs a recursive quick sort
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Todo ListBuild a Todo list that lets users add new tasks and delete existing tasks
Available frameworks
Topological SortImplement a function that performs a topological sort
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Traffic LightBuild a traffic light where the lights switch from green to yellow to red after predetermined intervals and loop indefinitely
Available frameworks
Deep CloneImplement a function that performs a deep copy of a value
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Digital ClockBuild a 7-segment digital clock that shows the current time
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Image CarouselBuild an image carousel that displays a sequence of images
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Job BoardBuild a job board that displays the latest job postings from Hacker News
Available frameworks
ClampPremiumImplement a function to clamp a number within the inclusive lower and upper bounds
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Function LengthPremiumImplement a function that returns the number of parameters expected by a function
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Number of ArgumentsPremiumImplement a function that returns the number of arguments it was called with
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SleepPremiumImplement a function that pauses for a specified duration before resuming execution
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Array.prototype.squarePremiumImplement a custom Array.prototype.square() method that squares the values in an array
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Cancellable IntervalPremiumImplement a function that acts like setInterval but returns a function to cancel the interval
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Cancellable TimeoutPremiumImplement a function that acts like setTimeout but returns a function to cancel the pending callback
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ChunkPremiumImplement a function that creates an array of elements split into smaller groups of a specified size
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CompactPremiumImplement a function that creates an array with all falsey values removed
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DifferencePremiumImplement a function that finds the difference in values between arrays
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Drop Right WhilePremiumImplement a function that excludes elements from the end of an array until the predicate returns false
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Drop WhilePremiumImplement a function that excludes elements from the beginning of an array until the predicate returns false
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FillPremiumImplement a function that fills an array with values within specified indices
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Find IndexPremiumImplement a function that returns the index of the first element in the array that satisfies the provided testing function
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Find Last IndexPremiumImplement a function that returns the index of the last element in the array that satisfies the provided testing function
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From PairsPremiumImplement a function that returns an object composed from key-value pairs
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Function.prototype.applyPremiumImplement the Function.prototype.apply() function that calls the function with a given `this` value and arguments as an array
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Function.prototype.callPremiumImplement the Function.prototype.call() function that calls the function with a given `this` value and provided arguments
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GetPremiumImplement a function to safely access deeply-nested properties in JavaScript objects
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In RangePremiumImplement a function to check if a number falls between two numbers
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IntersectionPremiumImplement a function that computes the intersection of arrays, returning a new array containing unique values present in all given arrays
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Max ByPremiumImplement a function that finds the maximum element based on the specified criteria
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Object MapPremiumImplement a function to transform values within an object
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OncePremiumImplement a function that accepts a callback and restricts its invocation to at most once
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Promise.rejectPremiumImplement a function to return a Promise object rejected with a reason
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RangePremiumImplement a function that returns a sequence of numbers in ascending order
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Range RightPremiumImplement a function that returns a sequence of numbers in descending order
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Selection SortPremiumImplement a function that performs a selection sort
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SingletonPremiumImplement a Singleton class that ensures a class has only one instance while providing a global point of access to that instance
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Unique ArrayPremiumImplement a function to remove all duplicate values from an array
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AccordionPremiumBuild an accordion component that a displays a list of vertically stacked sections with each containing a title and content snippet
ComposePremiumImplement a function that takes multiple functions as arguments and returns a new function that applies those functions in reverse
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Flight BookerPremiumBuild a component that books a flight for specified dates
Available frameworks
Function.prototype.bindPremiumImplement the Function.prototype.bind() function that creates a new function with the `this` keyword set to a provided value
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Generate TablePremiumGenerate a table of numbers given the rows and columns
Available frameworks
jQuery.cssPremiumImplement a jQuery-like function that sets the style of a DOM element
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Progress BarPremiumBuild a progress bar component that shows the percentage completion of an operation
Available frameworks
Progress BarsPremiumBuild a list of progress bars that fill up gradually when they are added to the page
Available frameworks
Promise.racePremiumImplement the Promise.race() function that resolves or rejects when any of the input elements are resolved or rejected
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SizePremiumImplement a function that returns the size of collection
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SumPremiumImplement a function that sums numbers by accepting a number and allows for repeated calling with more numbers until it is not called with any number
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Temperature ConverterPremiumBuild a temperature converter widget that converts temperature values between Celsius and Fahrenheit
Available frameworks
Make Counter IIPremiumImplement a function that returns a counter object with methods to retrieve and manipulate the value
CurryPremiumImplement a function that transforms a function that takes multiple arguments into a function that can be repeatedly called with only one argument at a time
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Group ByPremiumImplement a function that groups values in an array based on a function or property name
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Intersection ByPremiumImplement a function that returns an array of unique values that are included in all given arrays based on a provided iteratee function
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Intersection WithPremiumComputes the intersection of arrays using a custom comparator function to determine equality between elements
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Is EmptyPremiumImplement a function to check if a value is an empty object, collection, map, or set
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LimitPremiumImplement a function that accepts a callback and restricts its invocation to at most N times
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Promise MergePremiumImplement a function to merge the results of two promises into a single value
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Promise TimeoutPremiumImplement a function that resolves a promise if it is fulfilled within a timeout period and rejects otherwise
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Promise.resolvePremiumImplement a function to resolve a given value to a Promise
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Promise.withResolversPremiumImplement a function that returns an object containing a new `Promise` object and two functions to resolve or reject it
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PromisifyPremiumImplement a function that takes a function following the common error-first callback style and returns a version that returns promises
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Promisify IIPremiumImplement a promisify function that allows the original function to override the return value
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ThrottlePremiumImplement a function to control the execution of a function by limiting how many times it can execute over time
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TurtlePremiumImplement a Turtle class that moves a turtle on a 2D plane
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Union ByPremiumImplement a function that creates an array of unique values, in order, from all given arrays.
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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
Camel Case KeysPremiumImplement a function to convert all the keys in an object to camel case
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Compact IIPremiumImplement a function that returns an object with all falsey values removed
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Conforms ToPremiumImplement a function that checks if object conforms to source
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Curry IIPremiumImplement a function that transforms a function that takes multiple arguments into a function that can be repeatedly called with any number of arguments
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Data MergingPremiumImplement a function to merge rows of data from the same user
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Data Table IIPremiumBuild a users data table with sorting features
Available frameworks
Debounce IIPremiumImplement a debounce function that comes with a cancel method to cancel delayed invocations and a flush method to immediately invoke them
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Event Emitter IIPremiumImplement a class that can subscribe to and emit events that trigger attached callback functions. Subscription objects are returned and can unsubscribe itself
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File Explorer IIPremiumBuild a semi-accessible file explorer component that has the right ARIA roles, states, and properties
Available frameworks
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File Explorer IIIPremiumBuild a file explorer component using a flat DOM structure
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getElementsByStylePremiumImplement a function to get all DOM elements that are rendered using the specified style
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getElementsByTagNamePremiumImplement a function to get all DOM elements that match a tag
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Grid LightsPremiumBuild a grid of lights where the lights deactivate in the reverse order they were activated
Available frameworks
HTML SerializerPremiumImplement a function to serialize an object into an HTML string with indentation
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Identical DOM TreesPremiumImplement a function to determine if two DOM trees are the same
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jQuery Class ManipulationPremiumImplement a set of jQuery-like functions that manipulates classes on a DOM element
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JSON.stringifyPremiumImplement a function that converts a JavaScript value into a JSON string
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Like ButtonPremiumBuild a Like button that changes appearance based on the states
Available frameworks
List FormatPremiumImplement a function that formats a list of items into a single readable string
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Map AsyncPremiumImplement a function that maps an array of items with an asynchronous mapping function
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MemoizePremiumImplement a function that returns a memoized version of a function which accepts a single argument
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Modal Dialog IIPremiumBuild a semi-accessible modal dialog component that has the right ARIA roles, states, and properties
Available frameworks
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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
Promise.allSettledPremiumImplement the Promise.allSettled() function that resolves to an array of outcomes when all the input elements are either resolved or rejected
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Promise.anyPremiumImplement the Promise.any() function that resolves when any of the input elements are resolved
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Resumable IntervalPremiumImplement a function that creates a resumable interval object
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Squash ObjectPremiumImplement a function that returns a new object after squashing the input object into a single level of depth
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Star RatingPremiumBuild 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
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
Text SearchPremiumImplement a function to highlight text if a searched term appears within it
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HTMLJSTS
Deep EqualPremiumImplement a function that determines if two values are equal
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Deep MapPremiumImplement a function to recursively transform values
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getElementsByClassNamePremiumImplement a function to get all DOM elements that contain the specified classes
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Map Async LimitPremiumImplement a function that maps an array of items with an asynchronous mapping function while not exceeding the concurrency limit
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Progress Bars IIIPremiumBuild a list of progress bars that fill up gradually concurrently, up to a limit of 3
Available frameworks
Text Search IIPremiumImplement a function to highlight text if searched terms appear within it
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HTMLJSTS
Tic-tac-toePremiumBuild a tic-tac-toe game that is playable by two players
Available frameworks
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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
Deep MergePremiumImplement a function that merges two objects together
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Deep OmitPremiumImplement a function that removes specified keys and their corresponding values from an object, including nested objects or arrays
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Image Carousel IIPremiumBuild an image carousel that smoothly transitions between images
Available frameworks
Memoize IIPremiumImplement a function that returns a memoized version of a function which accepts any number of arguments
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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
StopwatchPremiumBuild a stopwatch widget that can measure how much time has passed
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Transfer ListPremiumBuild a component that allows transferring of items between two lists
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Undoable CounterPremiumBuild a counter with a history of the values and ability to undo/redo actions
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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
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Memory GamePremiumBuild a memory game where the player needs to match pairs of cards
Available frameworks
Curry IIIPremiumImplement a function which transforms a function which takes variadic arguments into a function that can be repeatedly called with any number of arguments
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Auth Code InputPremiumBuild an auth code input component that allows users to enter a 6-digit authorization code
Available frameworks
Classnames IIPremiumImplement a function that conditionally joins CSS class names together and also handles de-duplication and function values
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CSSJSTS
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
Backbone ModelPremiumImplement a class resembling Backbone.Model which allows storing of attributes/values and responding to changes in specific attribute values
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Data SelectionPremiumImplement a function to filter rows of data matching a specified requirement
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Data Table IIIPremiumBuild a generalized data table with pagination and sorting features
Modal Dialog IVPremiumBuild a fully-accessible modal dialog component that supports all required keyboard interactions
Available frameworks
Table of ContentsPremiumImplement a function to construct a table of contents from an HTML document
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HTMLJSTS
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Data Table IVPremiumBuild a generalized data table with pagination, sorting and filtering features
Available frameworks
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Image Carousel IIIPremiumBuild an image carousel that smoothly transitions between images that has a minimal DOM footprint
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Nested CheckboxesPremiumBuild a nested checkboxes component with parent-child selection logic
Available frameworks
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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
Deep Clone IIPremiumImplement a function that performs a deep copy of a value, but also handles circular references
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JSON.stringify IIPremiumImplement a function that converts a JavaScript value into a JSON string
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WordlePremiumBuild Wordle, the word-guessing game that took the world by storm