throttle.ts
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import { Operator } from '../Operator';
import { Observable, SubscribableOrPromise } from '../Observable';
import { Subscriber } from '../Subscriber';
import { Subscription, TeardownLogic } from '../Subscription';
import { OuterSubscriber } from '../OuterSubscriber';
import { InnerSubscriber } from '../InnerSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
/**
* Emits a value from the source Observable, then ignores subsequent source
* values for a duration determined by another Observable, then repeats this
* process.
*
* <span class="informal">It's like {@link throttleTime}, but the silencing
* duration is determined by a second Observable.</span>
*
* <img src="./img/throttle.png" width="100%">
*
* `throttle` emits the source Observable values on the output Observable
* when its internal timer is disabled, and ignores source values when the timer
* is enabled. Initially, the timer is disabled. As soon as the first source
* value arrives, it is forwarded to the output Observable, and then the timer
* is enabled by calling the `durationSelector` function with the source value,
* which returns the "duration" Observable. When the duration Observable emits a
* value or completes, the timer is disabled, and this process repeats for the
* next source value.
*
* @example <caption>Emit clicks at a rate of at most one click per second</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.throttle(ev => Rx.Observable.interval(1000));
* result.subscribe(x => console.log(x));
*
* @see {@link audit}
* @see {@link debounce}
* @see {@link delayWhen}
* @see {@link sample}
* @see {@link throttleTime}
*
* @param {function(value: T): Observable|Promise} durationSelector A function
* that receives a value from the source Observable, for computing the silencing
* duration for each source value, returned as an Observable or a Promise.
* @return {Observable<T>} An Observable that performs the throttle operation to
* limit the rate of emissions from the source.
* @method throttle
* @owner Observable
*/
export function throttle<T>(this: Observable<T>, durationSelector: (value: T) => SubscribableOrPromise<number>): Observable<T> {
return this.lift(new ThrottleOperator(durationSelector));
}
class ThrottleOperator<T> implements Operator<T, T> {
constructor(private durationSelector: (value: T) => SubscribableOrPromise<number>) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new ThrottleSubscriber(subscriber, this.durationSelector));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class ThrottleSubscriber<T, R> extends OuterSubscriber<T, R> {
private throttled: Subscription;
constructor(protected destination: Subscriber<T>,
private durationSelector: (value: T) => SubscribableOrPromise<number>) {
super(destination);
}
protected _next(value: T): void {
if (!this.throttled) {
this.tryDurationSelector(value);
}
}
private tryDurationSelector(value: T): void {
let duration: SubscribableOrPromise<number> = null;
try {
duration = this.durationSelector(value);
} catch (err) {
this.destination.error(err);
return;
}
this.emitAndThrottle(value, duration);
}
private emitAndThrottle(value: T, duration: SubscribableOrPromise<number>) {
this.add(this.throttled = subscribeToResult(this, duration));
this.destination.next(value);
}
protected _unsubscribe() {
const throttled = this.throttled;
if (throttled) {
this.remove(throttled);
this.throttled = null;
throttled.unsubscribe();
}
}
notifyNext(outerValue: T, innerValue: R,
outerIndex: number, innerIndex: number,
innerSub: InnerSubscriber<T, R>): void {
this._unsubscribe();
}
notifyComplete(): void {
this._unsubscribe();
}
}