work.suroh.tk/node_modules/rxjs/_esm2015/operators/sampleTime.js

80 lines
2.8 KiB
JavaScript

import { Subscriber } from '../Subscriber';
import { async } from '../scheduler/async';
/**
* Emits the most recently emitted value from the source Observable within
* periodic time intervals.
*
* <span class="informal">Samples the source Observable at periodic time
* intervals, emitting what it samples.</span>
*
* <img src="./img/sampleTime.png" width="100%">
*
* `sampleTime` periodically looks at the source Observable and emits whichever
* value it has most recently emitted since the previous sampling, unless the
* source has not emitted anything since the previous sampling. The sampling
* happens periodically in time every `period` milliseconds (or the time unit
* defined by the optional `scheduler` argument). The sampling starts as soon as
* the output Observable is subscribed.
*
* @example <caption>Every second, emit the most recent click at most once</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.sampleTime(1000);
* result.subscribe(x => console.log(x));
*
* @see {@link auditTime}
* @see {@link debounceTime}
* @see {@link delay}
* @see {@link sample}
* @see {@link throttleTime}
*
* @param {number} period The sampling period expressed in milliseconds or the
* time unit determined internally by the optional `scheduler`.
* @param {Scheduler} [scheduler=async] The {@link IScheduler} to use for
* managing the timers that handle the sampling.
* @return {Observable<T>} An Observable that emits the results of sampling the
* values emitted by the source Observable at the specified time interval.
* @method sampleTime
* @owner Observable
*/
export function sampleTime(period, scheduler = async) {
return (source) => source.lift(new SampleTimeOperator(period, scheduler));
}
class SampleTimeOperator {
constructor(period, scheduler) {
this.period = period;
this.scheduler = scheduler;
}
call(subscriber, source) {
return source.subscribe(new SampleTimeSubscriber(subscriber, this.period, this.scheduler));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class SampleTimeSubscriber extends Subscriber {
constructor(destination, period, scheduler) {
super(destination);
this.period = period;
this.scheduler = scheduler;
this.hasValue = false;
this.add(scheduler.schedule(dispatchNotification, period, { subscriber: this, period }));
}
_next(value) {
this.lastValue = value;
this.hasValue = true;
}
notifyNext() {
if (this.hasValue) {
this.hasValue = false;
this.destination.next(this.lastValue);
}
}
}
function dispatchNotification(state) {
let { subscriber, period } = state;
subscriber.notifyNext();
this.schedule(state, period);
}
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