What is it and Why it exists

What Is It

Piece of code (usually JavaScript on the Web) used to provide modern functionality on older browsers that do not natively support it.

Why Use It

• Mimic the functionalities of missing features
• address issues where browsers implement the same features in different ways

Implications

Native implementations of APIs can do more and are faster than polyfills

Creating Polyfills

// Assuming we want to use a log API
log("this API doesn't exist right now, but will in future")

// Above will avaluate to `uncaught ReferenceError: log is not defined`

// Patching (creating polyfill) to make API available
if (!window.log) {
	console.log("...patching);
	// define function on the fly
	window.log = msg => console.log(msg);
}