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
Languages
JSTS
Questions List
Make CounterImplement a function that accepts an integer value and returns a function that can be repeatedly called to return increasing values
Languages
JSTS
MeanImplement a function that finds the mean of the values inside an array
Languages
JSTS
Min ByImplement a function that finds the minimum element based on the specified criteria
Languages
JSTS
Type UtilitiesImplement utilities to determine primitive variable types in JavaScript
Languages
JSTS
CycleImplement a function that takes one or more values and returns a function that cycles through those values each time it is called
Languages
JSTS
Type Utilities IIImplement utilities to determine non-primitive variable types in JavaScript
Languages
JSTS
Count ByImplement a function that counts the number of times a value appears in an array based on a function or property name
Languages
JSTS
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
Languages
JSTS
ClassnamesImplement a function that conditionally joins CSS class names together
Languages
CSSJSTS
Event EmitterImplement a class that can subscribe to and emit events that trigger attached callback functions
Languages
JSTS
FlattenImplement a function that recursively flattens an array into a single level deep
Languages
JSTS
Promise.allImplement the Promise.all() function that resolves to an array of results if all the input elements are resolved or rejects otherwise
Languages
JSTS
Deep CloneImplement a function that performs a deep copy of a value
Languages
JSTS
ClampImplement a function to clamp a number within the inclusive lower and upper bounds
Languages
JSTS
Function LengthImplement a function that returns the number of parameters expected by a function
Languages
JSTS
Number of ArgumentsImplement a function that returns the number of arguments it was called with
Languages
JSTS
SleepImplement a function that pauses for a specified duration before resuming execution
Languages
JSTS
Array.prototype.squareImplement a custom Array.prototype.square() method that squares the values in an array
Languages
JSTS
Cancellable IntervalImplement a function that acts like setInterval but returns a function to cancel the interval
Languages
JSTS
Cancellable TimeoutImplement a function that acts like setTimeout but returns a function to cancel the pending callback
Languages
JSTS
ChunkImplement a function that creates an array of elements split into smaller groups of a specified size
Languages
JSTS
CompactImplement a function that creates an array with all falsey values removed
Languages
JSTS
DifferenceImplement a function that finds the difference in values between arrays
Languages
JSTS
Drop Right WhileImplement a function that excludes elements from the end of an array until the predicate returns false
Languages
JSTS
Drop WhileImplement a function that excludes elements from the beginning of an array until the predicate returns false
Languages
JSTS
FillImplement a function that fills an array with values within specified indices
Languages
JSTS
Find IndexImplement a function that returns the index of the first element in the array that satisfies the provided testing function
Languages
JSTS
Find Last IndexImplement a function that returns the index of the last element in the array that satisfies the provided testing function
Languages
JSTS
From PairsImplement a function that returns an object composed from key-value pairs
Languages
JSTS
Function.prototype.applyImplement the Function.prototype.apply() function that calls the function with a given `this` value and arguments as an array
Languages
JSTS
Function.prototype.callImplement the Function.prototype.call() function that calls the function with a given `this` value and provided arguments
Languages
JSTS
GetImplement a function to safely access deeply-nested properties in JavaScript objects
Languages
JSTS
In RangeImplement a function to check if a number falls between two numbers
Languages
JSTS
IntersectionImplement a function that computes the intersection of arrays, returning a new array containing unique values present in all given arrays
Languages
JSTS
Max ByImplement a function that finds the maximum element based on the specified criteria
Languages
JSTS
Object MapImplement a function to transform values within an object
Languages
JSTS
OnceImplement a function that accepts a callback and restricts its invocation to at most once
Languages
JSTS
Promise.rejectImplement a function to return a Promise object rejected with a reason
Languages
JSTS
RangeImplement a function that returns a sequence of numbers in ascending order
Languages
JSTS
Range RightImplement a function that returns a sequence of numbers in descending order
Languages
JSTS
SingletonImplement a Singleton class that ensures a class has only one instance while providing a global point of access to that instance
Languages
JSTS
Unique ArrayImplement a function to remove all duplicate values from an array
ComposeImplement a function that takes multiple functions as arguments and returns a new function that applies those functions in reverse
Languages
JSTS
Function.prototype.bindImplement the Function.prototype.bind() function that creates a new function with the `this` keyword set to a provided value
Languages
JSTS
jQuery.cssImplement a jQuery-like function that sets the style of a DOM element
Languages
HTMLCSSJSTS
Promise.raceImplement the Promise.race() function that resolves or rejects when any of the input elements are resolved or rejected
Languages
JSTS
SizeImplement a function that returns the size of collection
Languages
JSTS
SumImplement 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
Languages
JSTS
Make Counter IIImplement a function that returns a counter object with methods to retrieve and manipulate the value
CurryImplement 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
Languages
JSTS
Group ByImplement a function that groups values in an array based on a function or property name
Languages
JSTS
Intersection ByImplement a function that returns an array of unique values that are included in all given arrays based on a provided iteratee function
Languages
JSTS
Intersection WithComputes the intersection of arrays using a custom comparator function to determine equality between elements
Languages
JSTS
Is EmptyImplement a function to check if a value is an empty object, collection, map, or set
Languages
JSTS
LimitImplement a function that accepts a callback and restricts its invocation to at most N times
Languages
JSTS
Promise MergeImplement a function to merge the results of two promises into a single value
Languages
JSTS
Promise TimeoutImplement a function that resolves a promise if it is fulfilled within a timeout period and rejects otherwise
Languages
JSTS
Promise.resolveImplement a function to resolve a given value to a Promise
Languages
JSTS
Promise.withResolversImplement a function that returns an object containing a new `Promise` object and two functions to resolve or reject it
Languages
JSTS
PromisifyImplement a function that takes a function following the common error-first callback style and returns a version that returns promises
Languages
JSTS
Promisify IIImplement a promisify function that allows the original function to override the return value
Languages
JSTS
ThrottleImplement a function to control the execution of a function by limiting how many times it can execute over time
Languages
JSTS
TurtleImplement a Turtle class that moves a turtle on a 2D plane
Languages
JSTS
Union ByImplement a function that creates an array of unique values, in order, from all given arrays.
Languages
JSTS
Camel Case KeysImplement a function to convert all the keys in an object to camel case
Languages
JSTS
Compact IIImplement a function that returns an object with all falsey values removed
Languages
JSTS
Conforms ToImplement a function that checks if object conforms to source
Languages
JSTS
Curry IIImplement a function that transforms a function that takes multiple arguments into a function that can be repeatedly called with any number of arguments
Languages
JSTS
Data MergingImplement a function to merge rows of data from the same user
Languages
JSTS
Debounce IIImplement a debounce function that comes with a cancel method to cancel delayed invocations and a flush method to immediately invoke them
Languages
JSTS
Event Emitter IIImplement a class that can subscribe to and emit events that trigger attached callback functions. Subscription objects are returned and can unsubscribe itself
Languages
JSTS
getElementsByStyleImplement a function to get all DOM elements that are rendered using the specified style
Languages
HTMLCSSJSTS
getElementsByTagNameImplement a function to get all DOM elements that match a tag
Languages
HTMLJSTS
HTML SerializerImplement a function to serialize an object into an HTML string with indentation
Languages
HTMLJSTS
Identical DOM TreesImplement a function to determine if two DOM trees are the same
Languages
HTMLJSTS
jQuery Class ManipulationImplement a set of jQuery-like functions that manipulates classes on a DOM element
Languages
HTMLCSSJSTS
JSON.stringifyImplement a function that converts a JavaScript value into a JSON string
Languages
JSTS
List FormatImplement a function that formats a list of items into a single readable string
Languages
JSTS
Map AsyncImplement a function that maps an array of items with an asynchronous mapping function
Languages
JSTS
MemoizeImplement a function that returns a memoized version of a function which accepts a single argument
Languages
JSTS
Promise.allSettledImplement the Promise.allSettled() function that resolves to an array of outcomes when all the input elements are either resolved or rejected
Languages
JSTS
Promise.anyImplement the Promise.any() function that resolves when any of the input elements are resolved
Languages
JSTS
Resumable IntervalImplement a function that creates a resumable interval object
Languages
JSTS
Squash ObjectImplement a function that returns a new object after squashing the input object into a single level of depth
Languages
JSTS
Text SearchImplement a function to highlight text if a searched term appears within it
Languages
HTMLJSTS
Deep EqualImplement a function that determines if two values are equal
Languages
JSTS
Deep MapImplement a function to recursively transform values
Languages
JSTS
getElementsByClassNameImplement a function to get all DOM elements that contain the specified classes
Languages
HTMLCSSJSTS
Map Async LimitImplement a function that maps an array of items with an asynchronous mapping function while not exceeding the concurrency limit
Languages
JSTS
Text Search IIImplement a function to highlight text if searched terms appear within it
Languages
HTMLJSTS
Deep MergeImplement a function that merges two objects together
Languages
JSTS
Deep OmitImplement a function that removes specified keys and their corresponding values from an object, including nested objects or arrays
Languages
JSTS
Memoize IIImplement a function that returns a memoized version of a function which accepts any number of arguments
Languages
JSTS
Curry IIIImplement a function which transforms a function which takes variadic arguments into a function that can be repeatedly called with any number of arguments
Languages
JSTS
Classnames IIImplement a function that conditionally joins CSS class names together and also handles de-duplication and function values
Languages
CSSJSTS
Backbone ModelImplement a class resembling Backbone.Model which allows storing of attributes/values and responding to changes in specific attribute values
Languages
JSTS
Data SelectionImplement a function to filter rows of data matching a specified requirement