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

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

More about Array.prototype.some

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.


const array = [1, 2, 3, 4, 5];

// checks whether an element is even
const even = (element) => element % 2 === 0;

// expected output: true


The customSome takes two parameters

  1. callback function

Function to execute on each value in the array. The function is called with the following arguments:


  • The current element in the array.


  • The index (position) of the current element in the array.


  • The array that customFind was called on.

The callback must return a truthy value to indicate a matching element has been found.

  1. thisArg (Optional)

Object to use as this inside callbackFn.

customSome(callback, thisArg)

Return value

true if the callback function returns a truthy value for at least one element in the array. Otherwise, false.


Start the timer, complete your solution, and test it against the test cases provided by the platform. Ideally, you should finish this question within 30 mins. Share your solution with us --

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