Intent to Prototype and Ship: Streams API: ReadableStream async iteration
Mattias Buelens
Explainer
https://github.com/whatwg/streams/blob/main/readable-stream-async-iteration-explainer.md
Specification
https://streams.spec.whatwg.org/#rs-asynciterator
Summary
The streams APIs provide ubiquitous, interoperable primitives for creating, composing, and consuming streams of data. This change adds support for the async iterable protocol to the ReadableStream API, enabling readable streams to be used as the source of for await...of loops.
Blink component
Motivation
To consume a ReadableStream, developers currently acquire a reader and repeatedly call read(). By adding support for the async iterable protocol, web developers will be able to use the much simpler for await...of syntax to loop over all chunks of a ReadableStream.
Web developers are already using polyfills to async-iterate over a ReadableStream. These polyfills usually work fine, but might not handle all edge cases correctly (such as when the stream errors during a read, or releasing the reader's lock when breaking out of a for await...of loop).
Initial public proposal
None
Search tags
TAG review
None
TAG review status
Not applicable. (This is a small feature with a mature specification that's already shipping in Firefox.)
Risks
Interoperability and Compatibility
Low risk. The Streams API has already been standardised for a long time. Async iteration is already supported in one other browser (Firefox) and several JavaScript runtimes (Node.js, Deno, bun).
Gecko: Shipped/Shipping (https://bugzilla.mozilla.org/show_bug.cgi?id=1525852) Shipped in Firefox 110
WebKit: No signal (https://github.com/WebKit/standards-positions/issues/319)
Web developers: Positive (https://github.com/whatwg/streams/issues/778) Developers already expect this to work, and often use a polyfill.
Other signals:
Activation
Async iteration can be feature detected by checking the existence of `ReadableStream.prototype.values`. Various polyfills already exist in the wild. (e.g. https://jakearchibald.com/2017/async-iterators-and-generators/)
WebView application risks
Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?
None
Debuggability
No special support needed. The JavaScript debugger is already sufficiently capable of handling for await...of loops.
Is this feature fully tested by web-platform-tests?
Yes
https://wpt.fyi/results/streams/readable-streams/async-iterator.any.html
Flag name on chrome://flags
None
Finch feature name
ReadableStreamAsyncIterable
Requires code in //chrome?
False
Tracking bug
https://issues.chromium.org/issues/40612900
Estimated milestones
No milestones specified
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5143121161879552
This intent message was generated by Chrome Platform Status.
Yoav Weiss (@Shopify)
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Chris Harrelson
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Chris Harrelson
Thanks Chris, they're all blue now.Op woensdag 21 februari 2024 om 18:09:55 UTC+1 schreef chri...@google.com:
Mattias Buelens
Hi,
Domenic Denicola
To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOMQ%2Bw-YT%3DXY7xKC5htG%2B1yqqhYmpvXUxQ8qVX_zqdsVYXrHiw%40mail.gmail.com.