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feat(throttle): add higher-order lettable version of throttle
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,160 @@ | ||
| import { Operator } from '../Operator'; | ||
| import { Observable, SubscribableOrPromise } from '../Observable'; | ||
| import { Subscriber } from '../Subscriber'; | ||
| import { Subscription, TeardownLogic } from '../Subscription'; | ||
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| import { OuterSubscriber } from '../OuterSubscriber'; | ||
| import { InnerSubscriber } from '../InnerSubscriber'; | ||
| import { subscribeToResult } from '../util/subscribeToResult'; | ||
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| import { MonoTypeOperatorFunction } from '../interfaces'; | ||
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| export interface ThrottleConfig { | ||
| leading?: boolean; | ||
| trailing?: boolean; | ||
| } | ||
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| export const defaultThrottleConfig: ThrottleConfig = { | ||
| leading: true, | ||
| trailing: false | ||
| }; | ||
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| /** | ||
| * 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): SubscribableOrPromise} 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. | ||
| * @param {Object} config a configuration object to define `leading` and `trailing` behavior. Defaults | ||
| * to `{ leading: true, trailing: false }`. | ||
| * @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>(durationSelector: (value: T) => SubscribableOrPromise<number>, | ||
| config: ThrottleConfig = defaultThrottleConfig): MonoTypeOperatorFunction<T> { | ||
| return (source: Observable<T>) => source.lift(new ThrottleOperator(durationSelector, config.leading, config.trailing)); | ||
| } | ||
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| class ThrottleOperator<T> implements Operator<T, T> { | ||
| constructor(private durationSelector: (value: T) => SubscribableOrPromise<number>, | ||
| private leading: boolean, | ||
| private trailing: boolean) { | ||
| } | ||
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| call(subscriber: Subscriber<T>, source: any): TeardownLogic { | ||
| return source.subscribe( | ||
| new ThrottleSubscriber(subscriber, this.durationSelector, this.leading, this.trailing) | ||
| ); | ||
| } | ||
| } | ||
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| /** | ||
| * We need this JSDoc comment for affecting ESDoc | ||
| * @ignore | ||
| * @extends {Ignored} | ||
| */ | ||
| class ThrottleSubscriber<T, R> extends OuterSubscriber<T, R> { | ||
| private throttled: Subscription; | ||
| private _trailingValue: T; | ||
| private _hasTrailingValue = false; | ||
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| constructor(protected destination: Subscriber<T>, | ||
| private durationSelector: (value: T) => SubscribableOrPromise<number>, | ||
| private _leading: boolean, | ||
| private _trailing: boolean) { | ||
| super(destination); | ||
| } | ||
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| protected _next(value: T): void { | ||
| if (this.throttled) { | ||
| if (this._trailing) { | ||
| this._hasTrailingValue = true; | ||
| this._trailingValue = value; | ||
| } | ||
| } else { | ||
| const duration = this.tryDurationSelector(value); | ||
| if (duration) { | ||
| this.add(this.throttled = subscribeToResult(this, duration)); | ||
| } | ||
| if (this._leading) { | ||
| this.destination.next(value); | ||
| if (this._trailing) { | ||
| this._hasTrailingValue = true; | ||
| this._trailingValue = value; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| private tryDurationSelector(value: T): SubscribableOrPromise<any> { | ||
| try { | ||
| return this.durationSelector(value); | ||
| } catch (err) { | ||
| this.destination.error(err); | ||
| return null; | ||
| } | ||
| } | ||
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| protected _unsubscribe() { | ||
| const { throttled, _trailingValue, _hasTrailingValue, _trailing } = this; | ||
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| this._trailingValue = null; | ||
| this._hasTrailingValue = false; | ||
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| if (throttled) { | ||
| this.remove(throttled); | ||
| this.throttled = null; | ||
| throttled.unsubscribe(); | ||
| } | ||
| } | ||
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| private _sendTrailing() { | ||
| const { destination, throttled, _trailing, _trailingValue, _hasTrailingValue } = this; | ||
| if (throttled && _trailing && _hasTrailingValue) { | ||
| destination.next(_trailingValue); | ||
| this._trailingValue = null; | ||
| this._hasTrailingValue = false; | ||
| } | ||
| } | ||
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| notifyNext(outerValue: T, innerValue: R, | ||
| outerIndex: number, innerIndex: number, | ||
| innerSub: InnerSubscriber<T, R>): void { | ||
| this._sendTrailing(); | ||
| this._unsubscribe(); | ||
| } | ||
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| notifyComplete(): void { | ||
| this._sendTrailing(); | ||
| this._unsubscribe(); | ||
| } | ||
| } |