JavaScript - change values in array during foreach

In this article, we would like to show you how to change values in array during foreach in JavaScript.

Quick solution (ES6):

// ONLINE-RUNNER:browser;

const letters = ['a', 'b', 'c'];

letters.forEach((element, index, array) => array[index] = 'x');

console.log(letters); // [ 'x', 'x', 'x' ]

Alternative solution (ES5)

In this example, we alternatively use forEach() with a second argument (context), which will be used as the value of this in each call to the callback function.

// ONLINE-RUNNER:browser;

var letters = ['a', 'b', 'c'];

letters.forEach(function(element, index) {
    this[index] = 'x';
}, letters);

console.log(letters); // [ 'x', 'x', 'x' ]

Warning:

This solution won't work with arrow functions.

References

1. Array.prototype.forEach() - JavaScript | MDN