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The optional module installs support for Node.js and older browsers. is based on the HTML5 API provided by modern, evergreen browsers. Older browsers (mainly Edge and IE11) as well as versions of Node.js prior to v12 do not provide certain classes that depends on.

Note that while is designed to work seamlessly with other modules, using it is not a requirement. There are other good polyfill modules available on npm that can be used in its place.


npm install


Just import before you start using other modules.

import '';
import '';

To use the experimental Blob and File polyfills

import {installFilePolyfills} from '';

Included Polyfills

TextEncoder/TextDecoderNode.js < 11Yes (Older browsers)Only UTF8 is guaranteed to be supported
atob/btoaAll versionsNoNote: these functions are not unicode safe, but OK to use for test cases.
fetchAll versionsNoA subset of the fetch API is supported, see below.
ResponseAll versionsNoA subset of the Response API is supported, see below.
HeadersAll versionsNoA subset of the fetch API is supported, see below.
Blob (Experimental)All versionsNoA subset of the fetch API is supported, see below.
File (Experimental)All versionsNoA subset of the fetch API is supported, see below.
FileReader (Experimental)All versionsNoA subset of the fetch API is supported, see below.
ReadableStream (Experimental)All versionsNoA subset of the ReadableStream API is supported.

fetch Polyfill

The Node.js fetch, Response and Headers polyfills supports a large subset of the browser fetch API, including:

  • Response.text(), Response.arrayBuffer(), Response.json()
  • Response.body stream
  • headers, status, statusText etc.
  • data uri / base64 decoding
  • automatic gzip, brotli and deflate decompression support for responses with content-encoding headers.
  • Files ending with .gz are automatically decompressed with gzip decompression (this is only done on Node.js, in the browser the content-encoding header must be set).

The Node.js fetch is able to follow 30X redirect: if Response has status 300-399 and location header is set, the fetch polyfill re-requests data from location.

TextEncoder and TextDecoder Polyfills

TextEncoder and TextDecoder polyfills are provided to ensure these APIs are always available. In modern browsers these will evaluate to the built-in objects of the same name, however under Node.js polyfills are transparently installed.

Note: The provided polyfills only guarantee UTF8 support.


  • Applications should only install this module if they need to run under older environments. While the polyfills are only installed at runtime if the platform does not already support them, importing this module will increase the application's bundle size.
  • Refer to browser documentation for the usage of these classes, e.g. MDN.
  • In the browser, overhead of using these imports is not as high, as most polyfills are only bundled under Node.js.
  • If working under older browsers, e.g. IE11, you may need to install your own TextEncoder/TextDecoder polyfills before loading this library