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JavaScript Polyfills

Gain proficiency in front end fundamentals by implementing JavaScript and DOM APIs from scratch.

All Practice Questions

Coding Format

Questions List

  • Type UtilitiesImplement utilities to determine primitive variable types in JavaScript
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    JSTS
  • Type Utilities IIImplement utilities to determine non-primitive variable types in JavaScript
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    JSTS
  • Event EmitterImplement a class that can subscribe to and emit events that trigger attached callback functions
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    JSTS
  • FlattenImplement a function that recursively flattens an array into a single level deep
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    JSTS
  • 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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    JSTS
  • Find IndexImplement 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 IndexImplement a function that returns the index of the last element in the array that satisfies the provided testing function
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    JSTS
  • Function.prototype.applyImplement the Function.prototype.apply() function that calls the function with a given `this` value and arguments as an array
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    JSTS
  • Function.prototype.callImplement the Function.prototype.call() function that calls the function with a given `this` value and provided arguments
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  • Promise.rejectImplement a function to return a Promise object rejected with a reason
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  • Array.prototype.atImplement the Array.prototype.at() method
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  • Array.prototype.filterImplement the Array.prototype.filter() method
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  • Array.prototype.mapImplement the Array.prototype.map() method
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  • Array.prototype.reduceImplement the Array.prototype.reduce() method
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  • Function.prototype.bindImplement the Function.prototype.bind() function that creates a new function with the `this` keyword set to a provided value
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    JSTS
  • Promise.raceImplement the Promise.race() function that resolves or rejects when any of the input elements are resolved or rejected
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  • Array.prototype.concatImplement the Array.prototype.concat() method
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  • Promise.resolveImplement a function to resolve a given value to a Promise
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  • Promise.withResolversImplement a function that returns an object containing a new `Promise` object and two functions to resolve or reject it
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    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
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    JSTS
  • getElementsByTagNameImplement a function to get all DOM elements that match a tag
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    HTMLJSTS
  • JSON.stringifyImplement a function that converts a JavaScript value into a JSON string
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    JSTS
  • Promise.allSettledImplement 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.anyImplement the Promise.any() function that resolves when any of the input elements are resolved
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    JSTS
  • getElementsByClassNameImplement a function to get all DOM elements that contain the specified classes
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    HTMLCSSJSTS
  • getElementsByTagNameHierarchyImplement a function to get all DOM elements that match a tag hierarchy
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    HTMLJSTS