cheatsheets/polyfill.io.md

title, category, updated, layout, intro

title	category	updated	layout	intro
Polyfill.io	JavaScript libraries	2017-10-26	2017/sheet	[Polyfill.io](https://polyfill.io) is a service that serves JavaScript polyfills.

Usage

Default usage

<script src="https://cdn.polyfill.io/v2/polyfill.min.js"></script>

{: .-wrap}

This is the default script for Polyfill.io.

References

• API example (polyfill.io)
• List of features (polyfill.io)

Optimized

For modern browsers

<script>(function(d,s){
if(window.Promise&&[].includes&&Object.assign&&window.Map)return;
var sc=d.getElementsByTagName(s)[0],js=d.createElement(s);
js.src='https://cdn.polyfill.io/v2/polyfill.min.js';
sc.parentNode.insertBefore(js, sc);
}(document,'script'))</script>

This only includes polyfill.io when necessary, skipping it for modern browsers for faster load times.

Extra features

<script>(function(d,s){
if(window.fetch&&window.Promise&&[].includes&&Object.assign&&window.Map)return;
var sc=d.getElementsByTagName(s)[0],js=d.createElement(s);
js.src='https://cdn.polyfill.io/v2/polyfill.min.js?features=default,fetch';
sc.parentNode.insertBefore(js, sc);
}(document,'script'))</script>

{: data-line="2,4"}

This is the same as the previous, but also adds a polyfill for window.fetch(). We add a window.fetch check and loads the additional fetch feature.