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/** @prettier */
import { MonoTypeOperatorFunction, SchedulerLike } from '../types';
import { executeSchedule } from '../util/executeSchedule';
import { operate } from '../util/lift';
import { createOperatorSubscriber } from './OperatorSubscriber';
/**
* Re-emits all notifications from source Observable with specified scheduler.
*
* <span class="informal">Ensure a specific scheduler is used, from outside of an Observable.</span>
*
* `observeOn` is an operator that accepts a scheduler as a first parameter, which will be used to reschedule
* notifications emitted by the source Observable. It might be useful, if you do not have control over
* internal scheduler of a given Observable, but want to control when its values are emitted nevertheless.
*
* Returned Observable emits the same notifications (nexted values, complete and error events) as the source Observable,
* but rescheduled with provided scheduler. Note that this doesn't mean that source Observables internal
* scheduler will be replaced in any way. Original scheduler still will be used, but when the source Observable emits
* notification, it will be immediately scheduled again - this time with scheduler passed to `observeOn`.
* An anti-pattern would be calling `observeOn` on Observable that emits lots of values synchronously, to split
* that emissions into asynchronous chunks. For this to happen, scheduler would have to be passed into the source
* Observable directly (usually into the operator that creates it). `observeOn` simply delays notifications a
* little bit more, to ensure that they are emitted at expected moments.
*
* As a matter of fact, `observeOn` accepts second parameter, which specifies in milliseconds with what delay notifications
* will be emitted. The main difference between {@link delay} operator and `observeOn` is that `observeOn`
* will delay all notifications - including error notifications - while `delay` will pass through error
* from source Observable immediately when it is emitted. In general it is highly recommended to use `delay` operator
* for any kind of delaying of values in the stream, while using `observeOn` to specify which scheduler should be used
* for notification emissions in general.
*
* ## Example
*
* Ensure values in subscribe are called just before browser repaint
*
* ```ts
* import { interval, observeOn, animationFrameScheduler } from 'rxjs';
*
* const someDiv = document.createElement('div');
* someDiv.style.cssText = 'width: 200px;background: #09c';
* document.body.appendChild(someDiv);
* const intervals = interval(10); // Intervals are scheduled
* // with async scheduler by default...
* intervals.pipe(
* observeOn(animationFrameScheduler) // ...but we will observe on animationFrame
* ) // scheduler to ensure smooth animation.
* .subscribe(val => {
* someDiv.style.height = val + 'px';
* });
* ```
*
* @see {@link delay}
*
* @param scheduler Scheduler that will be used to reschedule notifications from source Observable.
* @param delay Number of milliseconds that states with what delay every notification should be rescheduled.
* @return A function that returns an Observable that emits the same
* notifications as the source Observable, but with provided scheduler.
*/
export function observeOn<T>(scheduler: SchedulerLike, delay = 0): MonoTypeOperatorFunction<T> {
return operate((source, subscriber) => {
source.subscribe(
createOperatorSubscriber(
subscriber,
(value) => executeSchedule(subscriber, scheduler, () => subscriber.next(value), delay),
() => executeSchedule(subscriber, scheduler, () => subscriber.complete(), delay),
(err) => executeSchedule(subscriber, scheduler, () => subscriber.error(err), delay)
)
);
});
}