63 lines
2.0 KiB
TypeScript
63 lines
2.0 KiB
TypeScript
declare global {
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interface SymbolConstructor {
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readonly observable: symbol;
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}
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}
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/**
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@remarks
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The TC39 observable proposal defines a `closed` property, but some implementations (such as xstream) do not as of 10/08/2021.
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As well, some guideance on making an `Observable` do not include `closed` propery.
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@see https://github.com/tc39/proposal-observable/blob/master/src/Observable.js#L129-L130
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@see https://github.com/staltz/xstream/blob/6c22580c1d84d69773ee4b0905df44ad464955b3/src/index.ts#L79-L85
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@see https://github.com/benlesh/symbol-observable#making-an-object-observable
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@category Observable
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*/
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export type Unsubscribable = {
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unsubscribe(): void;
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};
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/**
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@category Observable
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*/
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type OnNext<ValueType> = (value: ValueType) => void;
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/**
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@category Observable
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*/
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type OnError = (error: unknown) => void;
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/**
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@category Observable
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*/
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type OnComplete = () => void;
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/**
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@category Observable
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*/
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export type Observer<ValueType> = {
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next: OnNext<ValueType>;
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error: OnError;
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complete: OnComplete;
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};
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/**
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Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
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@remarks
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The TC39 Observable proposal defines 2 forms of `subscribe()`:
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1. Three callback arguments: `subscribe(observer: OnNext<ValueType>, onError?: OnError, onComplete?: OnComplete): Unsubscribable;`
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2. A single `observer` argument: (as defined below)
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But `Observable` implementations have evolved to preferring case 2 and some implementations choose not to implement case 1. Therefore, an `ObservableLike` cannot be trusted to implement the first case. (xstream and hand built observerables often do not implement case 1)
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@see https://github.com/tc39/proposal-observable#observable
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@see https://github.com/tc39/proposal-observable/blob/master/src/Observable.js#L246-L259
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@see https://benlesh.com/posts/learning-observable-by-building-observable/
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@category Observable
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*/
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export interface ObservableLike<ValueType = unknown> {
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subscribe(observer?: Partial<Observer<ValueType>>): Unsubscribable;
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[Symbol.observable](): ObservableLike<ValueType>;
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}
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