WICG Observableの話

tc39/proposal-observable

かつてECMAScriptにObservableを入れようとした

宣言的にイベントストリームを扱うための汎用データ構造

code:js

function listen(element, eventName) {

return new Observable(observer => {

// Create an event handler which sends data to the sink

let handler = event => observer.next(event);

// Attach the event handler

element.addEventListener(eventName, handler, true);

// Return a cleanup function which will cancel the event stream

return () => {

// Detach the event handler from the element

element.removeEventListener(eventName, handler, true);

};

});

}

const subscription = listen(element, "keydown")

.filter(event => event.keyCode in keyCommands)

.subscribe(command => { /*...*/ });

subscription.unsubscribe();

賛同が得られず終了

wicg/observable

ブラウザ（DOM）APIとしてObservableを導入しようという提案

イベントをストリーム処理しやすくする

code:js

element

.when('click')

.filter((e) => e.target.matches('.foo'))

.map((e) => ({ x: e.clientX, y: e.clientY }))

.subscribe({ next: handleClickAtPoint });

経緯

Observables were first proposed to the platform in TC39 in May of 2015. The proposal failed to gain traction, in part due to some opposition that the API was suitable to be a language-level primitive. In an attempt to renew the proposal at a higher level of abstraction, a WHATWG DOM issue was filed in December of 2017. Despite ample developer demand, lots of discussion, and no strong objectors, the DOM Observables proposal sat mostly still for several years (with some flux in the API design) due to a lack of implementer prioritization.

Later in 2019, an attempt at reviving the proposal was made back at the original TC39 repository, which involved some API simplifications and added support for the synchronous "firehose" problem.

This repository is an attempt to again breathe life into the Observable proposal with the hope of shipping a version of it to the Web Platform.

既存のデータモデルとの関係

https://scrapbox.io/files/67568937482a60fb845d88cd.png

標準化に向けて

いったんはWHATWGが主導してDOM APIへの採用を目指す

ECMAScriptでの採用はその先の目標

現状

Chrome: In development

Firefox: No signal

Safari: No signal

https://www.youtube.com/watch?v=IMIVmCkwOT4