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50 lines
3.1 KiB
50 lines
3.1 KiB
2 years ago
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import { Observable } from '../Observable';
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import { IScheduler } from '../Scheduler';
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/**
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*
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* Re-emits all notifications from source Observable with specified scheduler.
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*
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* <span class="informal">Ensure a specific scheduler is used, from outside of an Observable.</span>
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*
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* `observeOn` is an operator that accepts a scheduler as a first parameter, which will be used to reschedule
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* notifications emitted by the source Observable. It might be useful, if you do not have control over
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* internal scheduler of a given Observable, but want to control when its values are emitted nevertheless.
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*
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* Returned Observable emits the same notifications (nexted values, complete and error events) as the source Observable,
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* but rescheduled with provided scheduler. Note that this doesn't mean that source Observables internal
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* scheduler will be replaced in any way. Original scheduler still will be used, but when the source Observable emits
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* notification, it will be immediately scheduled again - this time with scheduler passed to `observeOn`.
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* An anti-pattern would be calling `observeOn` on Observable that emits lots of values synchronously, to split
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* that emissions into asynchronous chunks. For this to happen, scheduler would have to be passed into the source
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* Observable directly (usually into the operator that creates it). `observeOn` simply delays notifications a
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* little bit more, to ensure that they are emitted at expected moments.
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*
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* As a matter of fact, `observeOn` accepts second parameter, which specifies in milliseconds with what delay notifications
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* will be emitted. The main difference between {@link delay} operator and `observeOn` is that `observeOn`
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* will delay all notifications - including error notifications - while `delay` will pass through error
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* from source Observable immediately when it is emitted. In general it is highly recommended to use `delay` operator
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* for any kind of delaying of values in the stream, while using `observeOn` to specify which scheduler should be used
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* for notification emissions in general.
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*
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* @example <caption>Ensure values in subscribe are called just before browser repaint.</caption>
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* const intervals = Rx.Observable.interval(10); // Intervals are scheduled
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* // with async scheduler by default...
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*
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* intervals
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* .observeOn(Rx.Scheduler.animationFrame) // ...but we will observe on animationFrame
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* .subscribe(val => { // scheduler to ensure smooth animation.
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* someDiv.style.height = val + 'px';
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* });
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*
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* @see {@link delay}
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*
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* @param {IScheduler} scheduler Scheduler that will be used to reschedule notifications from source Observable.
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* @param {number} [delay] Number of milliseconds that states with what delay every notification should be rescheduled.
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* @return {Observable<T>} Observable that emits the same notifications as the source Observable,
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* but with provided scheduler.
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*
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* @method observeOn
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* @owner Observable
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*/
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export declare function observeOn<T>(this: Observable<T>, scheduler: IScheduler, delay?: number): Observable<T>;
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