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This library allows websites to maintain compatibility with older browsers, which do not implement newer features. It does so using polyfills for small new features, plus functions to determine if a browser supports a set of features natively or with polyfills.

If you would like to see what features the browser you are currently using implements, you can visit the documentation site which displays a compatibility table that detects which features are natively supported in your browser.

How is this used on GitHub?

We use all of these polyfills on We also use the isSupported() function to determine if the browser meets a minimum set of functionality which we expect, browser that return false from isSupported() do not send errors or statistics to our backend monitoring.


$ npm install @github/browser-support



import {isSupported, isPolyfilled, apply} from '@github/browser-support'

// Check if a browser is supported
if (!isSupported()) {
  console.assert(isSupported() === true)
  console.assert(isPolyfilled() === true)


npm install
npm test


Adding polyfills

Please do not add any polyfills for ECMA features that are Stage 3 or below. We only wish to polyfill features from ECMAScript that are Stage 4 (about to be included in a new years specification) or already specified.

Removing polyfills

Polyfills should only be removed after consulting with the @github/web-systems who will determine if a polyfill can be removed. This code is designed to be kept lightweight, we do not want to ship dozens of kb of polyfills.

As a polyfill is removed, it may be worth adding feature detection to the baseSupport const, to ensure that our baseline moves with our browser support matrix.


Distributed under the MIT license. See LICENSE for details.