This Package Uses Fetch

If you've landed here from a JavaScript package's documentation, it means that the aforementioned package uses fetch internally, and wants to help you polyfill it if needed.

For more information on why we created this document, visit our blog post.

Do I need a polyfill?

Here's a brief definition of a polyfill:

A polyfill is a piece of code (usually JavaScript on the Web) used to provide modern functionality on older environments that do not natively support it.

In the case of fetch, this will primarily be:

• Browsers: Opera Mini & IE
• Server: Node v17 or lower

Therefore, if you fit one of the following scenarios:

• plan on using the package in a webapp, and you have data that indicates that your users might be on these older browsers (e.g. by importing your analytics into https://caniuse.com/ciu/import)
• plan on using the package in a Node.js server that's on v17 or below

then you might want to keep reading. Otherwise, you don't need to do anything!

Polyfills

There are many polyfills out there, but here are the ones we'll recommend:

• node implementation: node-fetch
• browser polyfill: whatwg-fetch

Adding polyfills

To polyfill fetch in the global scope, you'll have to do the following in your application's entry point (or at least, before the package that needs fetch is imported):

• server:

import fetch from 'node-fetch';
globalThis.fetch = fetch;

// only import the package _after_
import packageThatUsesFetch from 'package-that-uses-fetch';

• browser:

// browser
import 'whatwg-fetch';

// only import the package _after_
import packageThatUsesFetch from 'package-that-uses-fetch';

From then on, you're free to use the package as you see fit.