eps1lon / abortcontroller-polyfill

Polyfill for the AbortController DOM API and abortable fetch (stub that calls catch, doesn't actually abort request).

AbortController polyfill for abortable fetch()

Minimal stubs so that the AbortController DOM API for terminating fetch() requests can be used in browsers that doesn't yet implement it. This "polyfill" doesn't actually close the connection when the request is aborted, but it will call .catch() with err.name == 'AbortError' instead of .then().

const controller = new AbortController();
const signal = controller.signal;
fetch('/some/url', {signal})
  .then(res => res.json())
  .then(data => {
    // do something with "data"
  }).catch(err => {
    if (err.name == 'AbortError') {
      return;
    }
  });
// controller.abort(); // can be called at any time

You can read about the AbortController API in the DOM specification.

How to use

$ npm install --save abortcontroller-polyfill

If you're using webpack or similar, you then import it early in your client entrypoint .js file using

import 'abortcontroller-polyfill/dist/polyfill-patch-fetch'
// or:
require('abortcontroller-polyfill/dist/polyfill-patch-fetch')

Using it on browsers without fetch

If you need to support browsers where fetch is not available at all (for example Internet Explorer 11), you first need to install a fetch polyfill and then import the abortcontroller-polyfill afterwards.

The unfetch npm package offers a minimal fetch() implementation (though it does not offer for example a Request class). If you need a polyfill that implements the full Fetch specification, use the whatwg-fetch npm package instead. Typically you will also need to load a polyfill that implements ES6 promises, for example promise-polyfill, and of course you need to avoid ES6 arrow functions and template literals.

Example projects showing abortable fetch setup so that it works even in Internet Explorer 11, using both unfetch and GitHub fetch, is available here.

Using it along with 'create-react-app'

create-react-app enforces the no-undef eslint rule at compile time so if your version of eslint does not list AbortController etc as a known global for the browser environment, then you might run into an compile error like:

  'AbortController' is not defined  no-undef

This can be worked around by (temporarily, details here) adding a declaration like:

  const AbortController = window.AbortController;

Using the AbortController/AbortSignal without patching fetch

If you just want to polyfill AbortController/AbortSignal without patching fetch you can use:

import 'abortcontroller-polyfill/dist/abortcontroller-polyfill-only'

Using it on Node.js

You can either import it as a ponyfill without modifying globals:

const { AbortController, abortableFetch } = require('abortcontroller-polyfill/dist/cjs-ponyfill');
const { fetch } = abortableFetch(require('node-fetch'));
// or
// import { AbortController, abortableFetch } from 'abortcontroller-polyfill/dist/cjs-ponyfill';
// import _fetch from 'node-fetch';
// const { fetch } = abortableFetch(_fetch);

or if you're lazy

global.fetch = require('node-fetch');
require('abortcontroller-polyfill/dist/polyfill-patch-fetch');

If you also need a Request class with support for aborting you can do:

const { AbortController, abortableFetch } = require('abortcontroller-polyfill/dist/cjs-ponyfill');
const _nodeFetch = require('node-fetch');
const { fetch, Request } = abortableFetch({fetch: _nodeFetch, Request: _nodeFetch.Request});

const controller = new AbortController();
const signal = controller.signal;
controller.abort();
fetch(Request("http://api.github.com", {signal}))
  .then(r => r.json())
  .then(j => console.log(j))
  .catch(err => {
      if (err.name === 'AbortError') {
          console.log('aborted');
      }
  })

See also Node.js examples here

Using it on Internet Explorer 11 (MSIE11)

The abortcontroller-polyfill works on Internet Explorer 11. However, to use it you must first install separate polyfills for promises and for fetch(). For the promise polyfill, you can use the promise-polyfill package from npm, and for fetch() you can use either the whatwg-fetch npm package (complete fetch implementation) or the unfetch npm package (not a complete polyfill but it's only 500 bytes large and covers a lot of the basic use cases).

If you choose unfetch, the imports should be done in this order for example:

import 'promise-polyfill/src/polyfill';
import 'unfetch/polyfill';
import 'abortcontroller-polyfill';

See example code here.

Using it on Internet Explorer 8 (MSIE8)

The abortcontroller-polyfill works on Internet Explorer 8. However, since github-fetch only supports IE 10+ you need to use the fetch-ie8 npm package instead and also note that IE 8 only implements ES 3 so you need to use the es5-shim package (or similar). Finally, just like with IE 11 you also need to polyfill promises. One caveat is that CORS requests will not work out of the box on IE 8.

Here is a basic example of abortable fetch running in IE 8.

Contributors

• Martin Olsson
• Jimmy Wärting
• silverwind
• Rasmus Jacobsen
• João Vieira
• Cyril Auburtin
• Leonardo Apiwan
• Jake Champion
• Sai Srinivasan
• Ambar Lee

License

MIT