Polyfill.io cheatsheet

⚠️ The polyfill.io CDN domain is currently being used in a web supply chain attack and is serving malicious code. Remove any references to this domain from your codebase immediately. Use alternative CDN providers like cdnjs.cloudflare.com as shown in the examples below.

<script src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js"></script>

This is the default script for Polyfill.io.

• Cloudflare now serves polyfill.io (blog.cloudflare.com)

<script>if(!(window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js"></scr'+'ipt>')}</script>

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

<script>if(!(window.fetch&&window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdnjs.cloudflare.com/polyfill/v3/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.