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debounceTime.ts
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debounceTime.ts
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import { asyncScheduler } from '../scheduler/async';
import { Subscription } from '../Subscription';
import { MonoTypeOperatorFunction, SchedulerAction, SchedulerLike } from '../types';
import { operate } from '../util/lift';
import { OperatorSubscriber } from './OperatorSubscriber';
/**
* Emits a notification from the source Observable only after a particular time span
* has passed without another source emission.
*
* <span class="informal">It's like {@link delay}, but passes only the most
* recent notification from each burst of emissions.</span>
*
* ![](debounceTime.png)
*
* `debounceTime` delays notifications emitted by the source Observable, but drops
* previous pending delayed emissions if a new notification arrives on the source
* Observable. This operator keeps track of the most recent notification from the
* source Observable, and emits that only when `dueTime` has passed
* without any other notification appearing on the source Observable. If a new value
* appears before `dueTime` silence occurs, the previous notification will be dropped
* and will not be emitted and a new `dueTime` is scheduled.
* If the completing event happens during `dueTime` the last cached notification
* is emitted before the completion event is forwarded to the output observable.
* If the error event happens during `dueTime` or after it only the error event is
* forwarded to the output observable. The cache notification is not emitted in this case.
*
* This is a rate-limiting operator, because it is impossible for more than one
* notification to be emitted in any time window of duration `dueTime`, but it is also
* a delay-like operator since output emissions do not occur at the same time as
* they did on the source Observable. Optionally takes a {@link SchedulerLike} for
* managing timers.
*
* ## Example
* Emit the most recent click after a burst of clicks
* ```ts
* import { fromEvent } from 'rxjs';
* import { debounceTime } from 'rxjs/operators';
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(debounceTime(1000));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link audit}
* @see {@link auditTime}
* @see {@link debounce}
* @see {@link debounceTime}
* @see {@link sample}
* @see {@link sampleTime}
* @see {@link throttle}
* @see {@link throttleTime}
*
* @param {number} dueTime The timeout duration in milliseconds (or the time
* unit determined internally by the optional `scheduler`) for the window of
* time required to wait for emission silence before emitting the most recent
* source value.
* @param {SchedulerLike} [scheduler=async] The {@link SchedulerLike} to use for
* managing the timers that handle the timeout for each value.
* @return A function that returns an Observable that delays the emissions of
* the source Observable by the specified `dueTime`, and may drop some values
* if they occur too frequently.
*/
export function debounceTime<T>(dueTime: number, scheduler: SchedulerLike = asyncScheduler): MonoTypeOperatorFunction<T> {
return operate((source, subscriber) => {
let activeTask: Subscription | null = null;
let lastValue: T | null = null;
let lastTime: number | null = null;
const emit = () => {
if (activeTask) {
// We have a value! Free up memory first, then emit the value.
activeTask.unsubscribe();
activeTask = null;
const value = lastValue!;
lastValue = null;
subscriber.next(value);
}
};
function emitWhenIdle(this: SchedulerAction<unknown>) {
// This is called `dueTime` after the first value
// but we might have received new values during this window!
const targetTime = lastTime! + dueTime;
const now = scheduler.now();
if (now < targetTime) {
// On that case, re-schedule to the new target
activeTask = this.schedule(undefined, targetTime - now);
return;
}
emit();
}
source.subscribe(
new OperatorSubscriber(
subscriber,
(value: T) => {
lastValue = value;
lastTime = scheduler.now();
// Only set up a task if it's not already up
if (!activeTask) {
activeTask = scheduler.schedule(emitWhenIdle, dueTime);
}
},
() => {
// Source completed.
// Emit any pending debounced values then complete
emit();
subscriber.complete();
},
// Pass all errors through to consumer.
undefined,
() => {
// Teardown.
lastValue = activeTask = null;
}
)
);
});
}