mirror of https://github.com/jkjoy/sunpeiwen.git
136 lines
9.0 KiB
Markdown
136 lines
9.0 KiB
Markdown
# web-streams-polyfill
|
|
|
|
Web Streams, based on the WHATWG spec reference implementation.
|
|
|
|
[](https://travis-ci.com/MattiasBuelens/web-streams-polyfill)
|
|
[](https://www.npmjs.com/package/web-streams-polyfill)
|
|
[](https://github.com/MattiasBuelens/web-streams-polyfill/blob/master/LICENSE)
|
|
[](https://gitter.im/web-streams-polyfill/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
|
|
|
|
## Links
|
|
|
|
- [Official spec][spec]
|
|
- [Reference implementation][ref-impl]
|
|
|
|
## Usage
|
|
|
|
This library comes in multiple variants:
|
|
* `web-streams-polyfill`: a [ponyfill] that provides the stream implementations
|
|
without replacing any globals, targeting ES2015+ environments.
|
|
* ✅ Node 6+ through `import` or `require()`
|
|
* ✅ Modern web browsers through `import`/`export` or `<script type="module">`
|
|
* ✅ Web apps for modern browsers using a bundler (like webpack or Rollup)
|
|
* `web-streams-polyfill/es5`: a ponyfill targeting ES5+ environments.
|
|
* ✅ Legacy Node through `require()`
|
|
* ✅ Legacy web browsers through [AMD][amd]
|
|
* ✅ Web apps for legacy browsers using a bundler (like webpack or Rollup)
|
|
* `web-streams-polyfill/polyfill`: a polyfill that replaces the native stream implementations,
|
|
targeting ES2015+ environments.
|
|
* ✅ Modern web browsers through regular `<script>`
|
|
* `web-streams-polyfill/polyfill/es5`: a polyfill targeting ES5+ environments.
|
|
* ✅ Legacy web browsers through regular `<script>`
|
|
|
|
Each variant also includes TypeScript type definitions, compatible with the DOM type definitions for streams included in TypeScript.
|
|
|
|
In version 4, the list of variants was reworked to have more modern defaults and to reduce the download size of the package.
|
|
See the [migration guide][migrating] for more information.
|
|
|
|
Usage as a polyfill:
|
|
```html
|
|
<!-- option 1: hosted by unpkg CDN -->
|
|
<script src="https://unpkg.com/web-streams-polyfill/dist/polyfill.js"></script>
|
|
<!-- option 2: self hosted -->
|
|
<script src="/path/to/web-streams-polyfill/dist/polyfill.js"></script>
|
|
<script>
|
|
var readable = new ReadableStream();
|
|
</script>
|
|
```
|
|
Usage as a Node module:
|
|
```js
|
|
var streams = require("web-streams-polyfill");
|
|
var readable = new streams.ReadableStream();
|
|
```
|
|
Usage as a ponyfill from within a ES2015 module:
|
|
```js
|
|
import { ReadableStream } from "web-streams-polyfill";
|
|
const readable = new ReadableStream();
|
|
```
|
|
Usage as a polyfill from within an ES2015 module:
|
|
```js
|
|
import "web-streams-polyfill/polyfill";
|
|
const readable = new ReadableStream();
|
|
```
|
|
|
|
## Compatibility
|
|
|
|
The default and `polyfill` variants work in any ES2015-compatible environment.
|
|
|
|
The `es5` and `polyfill/es5` 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][promise-support]), you must first include a `Promise` polyfill
|
|
(e.g. [promise-polyfill][promise-polyfill]).
|
|
|
|
[Async iterable support for `ReadableStream`][rs-asynciterator] is available in all variants, but requires an ES2018-compatible environment or a polyfill for `Symbol.asyncIterator`.
|
|
|
|
[`WritableStreamDefaultController.signal`][ws-controller-signal] is available in all variants, but requires a global `AbortController` constructor. If necessary, consider using a polyfill such as [abortcontroller-polyfill].
|
|
|
|
## Compliance
|
|
|
|
The polyfill implements [version `e9355ce` (18 Apr 2022)][spec-snapshot] of the streams specification.
|
|
|
|
The polyfill is tested against the same [web platform tests][wpt] that are used by browsers to test their native implementations.
|
|
It aims to pass all tests, although it allows some exceptions for practical reasons:
|
|
* The default (ES2015) variant passes all of the tests, except for:
|
|
* The ["bad buffers and views" tests for readable byte streams][wpt-bad-buffers].
|
|
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][proposal-arraybuffer-transfer] to make it possible).
|
|
The reference implementation "cheats" on these tests [by making a copy instead][ref-impl-transferarraybuffer], but that is unacceptable for the polyfill's performance ([#3][issue-3]).
|
|
* The [test for the prototype of `ReadableStream`'s async iterator][wpt-async-iterator-prototype].
|
|
Retrieving the correct `%AsyncIteratorPrototype%` requires using an async generator (`async function* () {}`), which is invalid syntax before ES2018.
|
|
Instead, the polyfill [creates its own version][stub-async-iterator-prototype] which is functionally equivalent to the real prototype.
|
|
* The tests [with patched globals][wpt-rs-patched-global] and [with `Object.prototype.then`][wpt-then-interception].
|
|
These tests are meant for browsers to ensure user-land modifications cannot affect the internal logic of `pipeTo()` and `tee()`.
|
|
However, it's not reasonable or desirable for a user-land polyfill to try and isolate itself completely from using the global `Object`.
|
|
* Certain `pipeTo()` tests that require synchronous inspection of the stream's state ([1][wpt-pipe-sync-state-1], [2][wpt-pipe-sync-state-2]).
|
|
Because the polyfill uses the public `getReader()` and `getWriter()` API to implement `pipeTo()`, it can only *asynchronously* observe if and when a stream becomes closed or errored.
|
|
Therefore, when the readable and the writable end become errored *at the exact same time*, it's difficult for the polyfill to observe these state changes in exactly the same order.
|
|
* The ES5 variant passes the same tests as the ES2015 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:
|
|
* The `name` property of down-leveled constructors is incorrect.
|
|
* The `length` property of down-leveled constructors and methods with optional arguments is incorrect.
|
|
* Not all properties and methods are correctly marked as non-enumerable.
|
|
* Down-leveled class methods are not correctly marked as non-constructable.
|
|
|
|
The type definitions are compatible with the built-in stream types of TypeScript 3.3 and higher.
|
|
|
|
## Contributors
|
|
|
|
Thanks to these people for their work on [the original polyfill][creatorrr-polyfill]:
|
|
|
|
- Diwank Singh Tomer ([creatorrr](https://github.com/creatorrr))
|
|
- Anders Riutta ([ariutta](https://github.com/ariutta))
|
|
|
|
[spec]: https://streams.spec.whatwg.org
|
|
[ref-impl]: https://github.com/whatwg/streams
|
|
[ponyfill]: https://github.com/sindresorhus/ponyfill
|
|
[amd]: https://requirejs.org/docs/whyamd.html
|
|
[migrating]: https://github.com/MattiasBuelens/web-streams-polyfill/blob/v4.0.0-beta.3/MIGRATING.md
|
|
[promise-support]: https://kangax.github.io/compat-table/es6/#test-Promise
|
|
[promise-polyfill]: https://www.npmjs.com/package/promise-polyfill
|
|
[rs-asynciterator]: https://streams.spec.whatwg.org/#rs-asynciterator
|
|
[ws-controller-signal]: https://streams.spec.whatwg.org/#ws-default-controller-signal
|
|
[abortcontroller-polyfill]: https://www.npmjs.com/package/abortcontroller-polyfill
|
|
[spec-snapshot]: https://streams.spec.whatwg.org/commit-snapshots/e9355ce79925947e8eb496563d599c329769d315/
|
|
[wpt]: https://github.com/web-platform-tests/wpt/tree/6a46d9cb8d20c510a620141c721b81b460a4ee55/streams
|
|
[wpt-bad-buffers]: https://github.com/web-platform-tests/wpt/blob/6a46d9cb8d20c510a620141c721b81b460a4ee55/streams/readable-byte-streams/bad-buffers-and-views.any.js
|
|
[proposal-arraybuffer-transfer]: https://github.com/domenic/proposal-arraybuffer-transfer
|
|
[ref-impl-transferarraybuffer]: https://github.com/whatwg/streams/blob/e9355ce79925947e8eb496563d599c329769d315/reference-implementation/lib/abstract-ops/ecmascript.js#L16
|
|
[issue-3]: https://github.com/MattiasBuelens/web-streams-polyfill/issues/3
|
|
[wpt-async-iterator-prototype]: https://github.com/web-platform-tests/wpt/blob/6a46d9cb8d20c510a620141c721b81b460a4ee55/streams/readable-streams/async-iterator.any.js#L24
|
|
[stub-async-iterator-prototype]: https://github.com/MattiasBuelens/web-streams-polyfill/blob/v4.0.0-beta.3/src/lib/readable-stream/async-iterator.ts#L126-L134
|
|
[wpt-rs-patched-global]: https://github.com/web-platform-tests/wpt/blob/887350c2f46def5b01c4dd1f8d2eee35dfb9c5bb/streams/readable-streams/patched-global.any.js
|
|
[wpt-then-interception]: https://github.com/web-platform-tests/wpt/blob/cf33f00596af295ee0f207c88e23b5f8b0791307/streams/piping/then-interception.any.js
|
|
[wpt-pipe-sync-state-1]: https://github.com/web-platform-tests/wpt/blob/e1e713c842e54ea0a9410ddc988b63d0e1d31973/streams/piping/multiple-propagation.any.js#L30-L53
|
|
[wpt-pipe-sync-state-2]: https://github.com/web-platform-tests/wpt/blob/e1e713c842e54ea0a9410ddc988b63d0e1d31973/streams/piping/multiple-propagation.any.js#L114-L138
|
|
[creatorrr-polyfill]: https://github.com/creatorrr/web-streams-polyfill
|