How to implement Array.prototype.includes? JavaScript Interview Question | Problem Solving | JavaScript Polyfills
@Yomesh Gupta

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In this question, the candidate needs to implement a function customIncludes that mimics the behaviour of Array.prototype.includes method.

More about Array.prototype.includes

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.


const array = [5, 12, 8, 130, 44];
const found = array.customIncludes(5);

// prints true


The customIncludes takes two parameters

  1. searchElement

The value to search for.

  1. fromIndex (Optional)

The position in this array at which to begin searching for searchElement.

The first element to be searched is found at fromIndex for positive values of fromIndex, or at arr.length + fromIndex for negative values of fromIndex.

Defaults to 0.

Return value

A boolean value which is true if the value searchElement is found within the array (or the part of the array indicated by the index fromIndex, if specified).

array.customIncludes(searchElement, fromIndex);


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