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Web Streams, based on the WHATWG spec reference implementation.
This library comes in multiple variants:
web-streams-polyfill
: a polyfill that replaces the native stream implementations.
Recommended for use in web apps supporting older browsers through a <script>
tag.web-streams-polyfill/es6
: a polyfill targeting ES2015+ environments.
Recommended for use in web apps supporting modern browsers through a <script>
tag.web-streams-polyfill/es2018
: a polyfill targeting ES2018+ environments.web-streams-polyfill/ponyfill
: a ponyfill that provides
the stream implementations without replacing any globals.
Recommended for use in legacy Node applications, or in web libraries supporting older browsers.web-streams-polyfill/ponyfill/es6
: a ponyfill targeting ES2015+ environments.
Recommended for use in Node 6+ applications, or in web libraries supporting modern browsers.web-streams-polyfill/ponyfill/es2018
: a ponyfill targeting ES2018+ environments.
Recommended for use in Node 10+ applications.Each variant also includes TypeScript type definitions, compatible with the DOM type definitions for streams included in TypeScript.
Usage as a polyfill:
<!-- option 1: hosted by unpkg CDN -->
<script src="https://unpkg.com/web-streams-polyfill/dist/polyfill.min.js"></script>
<!-- option 2: self hosted -->
<script src="/path/to/web-streams-polyfill/dist/polyfill.min.js"></script>
<script>
var readable = new ReadableStream();
</script>
Usage as a Node module:
var streams = require("web-streams-polyfill/ponyfill");
var readable = new streams.ReadableStream();
Usage as a ES2015 module:
import { ReadableStream } from "web-streams-polyfill/ponyfill";
const readable = new ReadableStream();
The polyfill
and ponyfill
variants work in any ES5-compatible environment that has a global Promise
.
If you need to support older browsers or Node versions that do not have a native Promise
implementation
(check the support table), you must first include a Promise
polyfill
(e.g. promise-polyfill).
The polyfill/es6
and ponyfill/es6
variants work in any ES2015-compatible environment.
The polyfill/es2018
and ponyfill/es2018
variants work in any ES2018-compatible environment.
Async iterable support for ReadableStream
is available in all variants, but requires an ES2018-compatible environment or a polyfill for Symbol.asyncIterator
.
WritableStreamDefaultController.signal
is available in all variants, but requires a global AbortController
constructor. If necessary, consider using a polyfill such as abortcontroller-polyfill.
The polyfill implements version 4b6b93c
(25 Oct 2021) of the streams specification.
The polyfill is tested against the same web platform tests that are used by browsers to test their native implementations. The polyfill aims to pass all tests, although it allows some exceptions for practical reasons:
es2018
variant passes all of the tests, except for the "bad buffers and views" tests for readable byte streams.
These tests require the implementation to synchronously transfer the contents of an ArrayBuffer
, which is not yet possible from JavaScript (although there is a proposal to make it possible).
The reference implementation "cheats" on these tests by making a copy instead, but that is unacceptable for the polyfill's performance (#3).es6
variant passes the same tests as the es2018
variant, except for the test for the prototype of ReadableStream
's async iterator.
Retrieving the correct %AsyncIteratorPrototype%
requires using an async generator (async function* () {}
), which is invalid syntax before ES2018.
Instead, the polyfill creates its own version which is functionally equivalent to the real prototype.es5
variant passes the same tests as the es6
variant, except for various tests about specific characteristics of the constructors, properties and methods.
These test failures do not affect the run-time behavior of the polyfill.
For example:
name
property of down-leveled constructors is incorrect.length
property of down-leveled constructors and methods with optional arguments is incorrect.The type definitions are compatible with the built-in stream types of TypeScript 3.3.
Thanks to these people for their work on the original polyfill: