cheatsheets/polyfill.io.md

title	category	updated	intro
Polyfill.io	JavaScript libraries	2018-08-20	[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>if(!(window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v2/polyfill.min.js"></scr'+'ipt>')}</script>

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

Extra features

<script>if(!(window.fetch&&window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=default,fetch"></scr'+'ipt>')}</script>

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.