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Polyfills in JavaScript

What are Polyfills?

Polyfills are code snippets that provide missing functionality to older web browsers. They spawned similarly to AJAX, as the need for something new and advanced was already there. With polyfills, developers could write code that uses the latest web standards while addressing the missing functionalities.

The Origin and History of Polyfills

In 2009, Remy Sharp coined the term "polyfill." He intended to explain his need to replicate an API using JavaScript that the browser doesn't support natively.

He didn't mean for it to become a standardized term, but the community found it apt, and it quickly got to mass adoption.

In simple terms, "poly" refers to the various techniques used to achieve the same goal, and "fill" means filling the gap between what a web browser provides and what a developer requires.

In the early days of the web, web engineers had to write different code for different web browsers to ensure that their web applications worked correctly.

With the rise of modern web browsers and standards, the problem became less pronounced. However, not all web browsers have adopted the latest web standards, and some continue to interpret them differently.

Enter Polyfills.

The Impact of jQuery

jQuery was a game-changer in the world of web development. Upon its release in 2006, it made JavaScript development much more accessible.

However, the main contribution was acting as a polyfill for many of the inconsistencies across different browsers. jQuery filled those gaps and provided a consistent API for developers to work with.

In many ways, jQuery was the first popular polyfill library, opening the door for future polyfill libraries to emerge. It granted developers the space to focus on building their applications and worrying less about cross-browser compatibility issues.

Polyfill Libraries

Each polyfill library is geared for specific purposes and addresses specific problems. Some of the most common ones include core.js and HTML5 Shiv. They provide a comprehensive set of polyfills for modern JavaScript APIs and HTML5 features that are not yet fully supported by older browsers.

  • Core.js, for example, is a modular and customizable polyfill library that covers a wide range of modern JavaScript features. With a relatively small footprint, it's neatly optimized for performance.

  • HTML5 Shiv is specifically designed for styling HTML5 elements in older browsers. For instance, older versions of IE don't recognize HTML5 elements as block-level elements, making it difficult to style them correctly.

Both of these libraries ensure cross-browser compatibility without having to write and maintain custom polyfills. Moreover, they make web applications accessible to a larger number of users.

Polyfill Examples

Let's demonstrate how polyfills provide support for modern features that aren't natively supported by certain web browsers.

With the whatwg-fetch polyfill, we can make network requests and handle responses even on Internet Explorer which doesn't natively support the fetch API.

import 'whatwg-fetch';

  .then(response => response.json())
  .then(data => {

Final Thoughts

Now, let's not forget that web development can sometimes be a bumpy ride, and Polyfills are no exception. While they can work wonders, there's always a risk of subtle differences in behavior and performance compared to the native implementation. So, it's crucial to use them cautiously and research relevant community forums and repository documentation to understand them thoroughly.