Polyfill

A polyfill is a piece of code written in JavaScript that replicates the functionality of a browser feature that is not supported by a particular browser version, allowing websites to work across different browsers and their versions.

Polyfills can be used to add support for new web technologies or to fallback to older ones that have been phased out by newer browsers. They are essentially a way of filling in the gaps left by older browsers that do not support the latest web standards.

Purpose

Polyfills are designed to help web developers to create websites that work consistently across different browsers and their versions, without needing to write separate code for each browser. They allow developers to leverage the latest web technologies and features, even if they are not natively supported by a particular browser.

The main purpose of polyfill is to ensure that websites work on older browsers that do not have the latest web technologies, thus improving browser compatibility. With polyfills, developers can write code that works the same way on all browsers, even if they are using different versions.

Usage

Polyfills are used to add support for new web technologies or to fallback to older ones that have been phased out by newer browsers. They are typically included as JavaScript files in the head section of a web page, and they are loaded before the rest of the page’s JavaScript.

When a browser encounters a web page that uses a feature that is not supported by its version, it will look for a polyfill that replicates that feature. If the polyfill is found, the browser will use it to provide the missing functionality. If the polyfill is not found, the feature will simply not work.

Polyfills are often used in conjunction with feature detection techniques, such as Modernizr, which check whether a browser supports a certain feature before attempting to use it. If the feature is not supported, the polyfill is loaded to provide the missing functionality.

Examples of Polyfills

There are many polyfills available for different web technologies and features. Here are a few examples:

Fetch Polyfill

The Fetch API is a modern replacement for XMLHttpRequest (XHR), which allows developers to make HTTP requests from JavaScript. However, it is not supported by all browsers, particularly older ones.

The Fetch polyfill provides a way to use the Fetch API on browsers that do not support it. It replicates the functionality of the Fetch API, allowing developers to use the same code on all browsers.

Object.assign Polyfill

Object.assign is a JavaScript method that allows developers to copy the values of all enumerable properties from one or more source objects to a target object. It is a useful way to merge objects or to create new ones.

However, Object.assign is not supported by all browsers, particularly older ones. The Object.assign polyfill provides a way to use the Object.assign method on browsers that do not support it. It replicates the functionality of the method, allowing developers to use the same code on all browsers.

ES6 Array Methods Polyfill

ES6 introduced several new methods to the Array object, such as map(), filter(), and reduce(). These methods provide a more functional approach to working with arrays.

However, these methods are not supported by all browsers, particularly older ones. The ES6 Array Methods polyfill provides a way to use these methods on browsers that do not support them. It replicates the functionality of the methods, allowing developers to use the same code on all browsers.