node package manager


Size Support
2 KB > IE8


Version 1.0.0 introduced breaking changes.
Please check How to use? for more information.

What's the use?

Made for easier use of the API to detect browser support, offer dynamic polyfills and save an extra HTTP request.

Write modern code like fetch, Promise or Array.prototype.includes without the need to transform it or locally load a polyfill.

Note: Does not polyfill syntactic sugar like Classes, enhanced Object literals and features like Arrow Functions or Template Strings. Use compilers like Babel for that.

How does it work?

The module tests the given functions in fills (see below) against the window to check if the browser supports everything.

If not, it creates a link like, inserts a script tag to make the HTTP request and loads only the needed polyfills.
The tag is put at the bottom of the page with the async attribute.

How to use?

NPM: npm i dynamic-polyfill -S
Yarn: yarn add dynamic-polyfill

import polyfill from 'dynamic-polyfill'
// or use require:
// const polyfill = require('dynamic-polyfill')
    fills: ['fetch', 'Array.prototype.includes'],
    options: ['gated', 'always'],
    minify: false,
    rum: false,
    afterFill() {
        // callback

Note: As of now not all available API options are supported here. Take a look at the full reference list.


['fetch', 'Array.prototype.includes'] (default: empty)
A list of what can be polyfilled.
Put them in an array of strings. If empty, as default marked features on the website are being used.


['gated', 'always'] (default: empty)

Polyfill should be included regardless of whether it is required by the user-agent making the request. If there are multiple browser-specific variants of the polyfill, the default one will be used for browser that doesn't actually require the polyfill. In some cases where the only way of implementing a polyfill is to use browser-specific proprietary technology, the default variant may be empty.

If the polyfill is included in the bundle, it will be accompanied by a feature detect, which will only execute the polyfill if the native API is not present.


true | false (default: true)
Set to false for deeper insight of what is being polyfilled.

Real User Monitoring

rum: false (default: true)
Allows the polyfill service to gather performance data about itself using the resource timing API and to perform feature detection to improve our browser targeting.

More info under rum.

The service will default it to true in the future hence the module default choice. Set rum: false if you want to opt out.

After Fill

Put your modern code in this callback to make sure the polyfills are loaded first.


    fills: ['fetch'],
    afterFill() {
function main() {
        .then(res => res.json())

Usage in IE8

For usage in IE8, you need a polyfill for Array.prototype.reduce(). You may copy the polyfill code from MDN.