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JavaScript Polyfills

Number of questions
22 questions
Recommended duration to spend during interviews
355 mins
Gain proficiency in front end fundamentals by implementing JavaScript and DOM APIs from scratch.

All Practice Questions

Coding Format
Number of questions
22 questions
Total time
6 hours total

Questions List

  • 1
    Type UtilitiesImplement utilities to determine primitive variable types in JavaScript
    Difficulty
    Easy
    Languages
    JSTS
  • 2
    Type Utilities IIImplement utilities to determine non-primitive variable types in JavaScript
    Difficulty
    Easy
    Languages
    JSTS
  • 3
    Event EmitterImplement a class that can subscribe to and emit events that trigger attached callback functions
    Difficulty
    Medium
    Languages
    JSTS
  • 4
    FlattenImplement a function that recursively flattens an array into a single level deep
    Difficulty
    Medium
    Languages
    JSTS
  • 5
    Promise.allImplement the Promise.all() function that resolves to an array of results if all the input elements are resolved or rejects otherwise
    Difficulty
    Medium
    Languages
    JSTS
  • Find IndexImplement a function that returns the index of the first element in the array that satisfies the provided testing function
    Difficulty
    Easy
    Languages
    JSTS
  • Find Last IndexImplement a function that returns the index of the last element in the array that satisfies the provided testing function
    Difficulty
    Easy
    Languages
    JSTS
  • Function.prototype.applyImplement the Function.prototype.apply() function that calls the function with a given `this` value and arguments as an array
    Difficulty
    Easy
    Languages
    JSTS
  • Function.prototype.callImplement the Function.prototype.call() function that calls the function with a given `this` value and provided arguments
    Difficulty
    Easy
    Languages
    JSTS
  • Array.prototype.atImplement the Array.prototype.at() method
    Difficulty
    Easy
    Languages
    JSTS
  • Array.prototype.filterImplement the Array.prototype.filter() method
    Difficulty
    Easy
    Languages
    JSTS
  • Array.prototype.mapImplement the Array.prototype.map() method
    Difficulty
    Easy
    Languages
    JSTS
  • Array.prototype.reduceImplement the Array.prototype.reduce() method
    Difficulty
    Easy
    Languages
    JSTS
  • Function.prototype.bindImplement the Function.prototype.bind() function that creates a new function with the `this` keyword set to a provided value
    Difficulty
    Easy
    Languages
    JSTS
  • Promise.raceImplement the Promise.race() function that resolves or rejects when any of the input elements are resolved or rejected
    Difficulty
    Easy
    Languages
    JSTS
  • New
    Array.prototype.concatImplement the Array.prototype.concat() method
    Difficulty
    Medium
    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
    Difficulty
    Medium
    Languages
    JSTS
  • getElementsByTagNameImplement a function to get all DOM elements that match a tag
    Difficulty
    Medium
    Languages
    HTMLJSTS
  • JSON.stringifyImplement a function that converts a JavaScript value into a JSON string
    Difficulty
    Medium
    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
    Difficulty
    Medium
    Languages
    JSTS
  • Promise.anyImplement the Promise.any() function that resolves when any of the input elements are resolved
    Difficulty
    Medium
    Languages
    JSTS
  • getElementsByClassNameImplement a function to get all DOM elements that contain the specified classes
    Difficulty
    Medium
    Languages
    HTMLCSSJSTS