45 lines
2.0 KiB
TypeScript
45 lines
2.0 KiB
TypeScript
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import { Observable } from '../Observable';
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/**
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* Converts a higher-order Observable into a first-order Observable by
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* subscribing to only the most recently emitted of those inner Observables.
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*
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* <span class="informal">Flattens an Observable-of-Observables by dropping the
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* previous inner Observable once a new one appears.</span>
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*
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* <img src="./img/switch.png" width="100%">
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*
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* `switch` subscribes to an Observable that emits Observables, also known as a
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* higher-order Observable. Each time it observes one of these emitted inner
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* Observables, the output Observable subscribes to the inner Observable and
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* begins emitting the items emitted by that. So far, it behaves
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* like {@link mergeAll}. However, when a new inner Observable is emitted,
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* `switch` unsubscribes from the earlier-emitted inner Observable and
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* subscribes to the new inner Observable and begins emitting items from it. It
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* continues to behave like this for subsequent inner Observables.
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*
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* @example <caption>Rerun an interval Observable on every click event</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* // Each click event is mapped to an Observable that ticks every second
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* var higherOrder = clicks.map((ev) => Rx.Observable.interval(1000));
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* var switched = higherOrder.switch();
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* // The outcome is that `switched` is essentially a timer that restarts
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* // on every click. The interval Observables from older clicks do not merge
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* // with the current interval Observable.
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* switched.subscribe(x => console.log(x));
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*
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* @see {@link combineAll}
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* @see {@link concatAll}
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* @see {@link exhaust}
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* @see {@link mergeAll}
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* @see {@link switchMap}
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* @see {@link switchMapTo}
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* @see {@link zipAll}
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*
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* @return {Observable<T>} An Observable that emits the items emitted by the
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* Observable most recently emitted by the source Observable.
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* @method switch
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* @name switch
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* @owner Observable
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*/
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export declare function _switch<T>(this: Observable<Observable<T>>): Observable<T>;
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