Polyfills in JavaScript

In JavaScript, a polyfill is a piece of code (usually a JavaScript script) that provides modern functionality to older browsers or environments that lack support for certain features.
Polyfills help bridge the gap between what’s available in modern JavaScript and what’s supported in older browsers, allowing developers to use newer features
without worrying about compatibility issues.

Why use polyfills?

Cross-browser compatibility: Different browsers and versions may support different JavaScript features. Polyfills enable you to write code using the latest JavaScript features and ensure it works consistently across various browsers.

Progressive Enhancement: You can use modern features while still supporting older browsers, offering a better user experience for users with modern browsers but basic functionality for users with older browsers.

Code Maintainability: Instead of writing separate code for different browser versions, polyfills centralize the handling of feature support, making your codebase cleaner and easier to

Future-proofing: As new JavaScript features are introduced, you can start using them with polyfills before native support becomes widespread.

How to use a polyfill:

To use a polyfill, you typically follow these steps:

Feature Detection:
Before applying a polyfill, it’s essential to check if the feature is natively supported by the browser. This process is known as feature detection. You can use various methods for feature detection, such as type of, in, or hasOwnProperty, or even libraries like Modernizr.

Conditionally load the polyfill:
If the feature is not supported, you load the polyfill script, which
provides the missing functionality. You can conditionally load the
polyfill based on the result of the feature detection check.

Let’s implement polyfills for three commonly used array methods:

map, filter, and forEach.
Polyfill for Array.prototype.map:
if (!Array.prototype.map)
{ Array.prototype.map = function (callback, thisArg) {
var arr = this;
var mappedArray = []; for (var i = 0; i < arr.length; i++) {
mappedArray.push(callback.call(thisArg, arr[i], i, arr)); }
return mappedArray; };
Polyfill for Array.prototype.filter:
if (!Array.prototype.filter) {
Array.prototype.filter = function (callback, thisArg) {
var arr = this;
var filteredArray = [];
for (var i = 0; i < arr.length; i++) {
if (callback.call(thisArg, arr[i], i, arr)) {
return filteredArray;

Polyfill for Array.prototype.forEach:

if (!Array.prototype.forEach) {
Array.prototype.forEach = function (callback, thisArg) {
var arr = this;
for (var i = 0; i < arr.length; i++) {
callback.call(thisArg, arr[i], i, arr);


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