feat(sampleTime): add higher-order lettable version of sampleTime

src/operator/sampleTime.ts

@@ -1,10 +1,7 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
 import { IScheduler } from '../Scheduler';
-import { Action } from '../scheduler/Action';
 import { async } from '../scheduler/async';
-import { TeardownLogic } from '../Subscription';
+import { sampleTime as higherOrder } from '../operators/sampleTime';
 
 /**
  * Emits the most recently emitted value from the source Observable within
@@ -43,50 +40,5 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 export function sampleTime<T>(this: Observable<T>, period: number, scheduler: IScheduler = async): Observable<T> {
-  return this.lift(new SampleTimeOperator(period, scheduler));
-}
-
-class SampleTimeOperator<T> implements Operator<T, T> {
-  constructor(private period: number,
-              private scheduler: IScheduler) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new SampleTimeSubscriber(subscriber, this.period, this.scheduler));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class SampleTimeSubscriber<T> extends Subscriber<T> {
-  lastValue: T;
-  hasValue: boolean = false;
-
-  constructor(destination: Subscriber<T>,
-              private period: number,
-              private scheduler: IScheduler) {
-    super(destination);
-    this.add(scheduler.schedule(dispatchNotification, period, { subscriber: this, period }));
-  }
-
-  protected _next(value: T) {
-    this.lastValue = value;
-    this.hasValue = true;
-  }
-
-  notifyNext() {
-    if (this.hasValue) {
-      this.hasValue = false;
-      this.destination.next(this.lastValue);
-    }
-  }
-}
-
-function dispatchNotification<T>(this: Action<any>, state: any) {
-  let { subscriber, period } = state;
-  subscriber.notifyNext();
-  this.schedule(state, period);
+  return higherOrder(period, scheduler)(this);
 }

src/operators/index.ts

@@ -59,6 +59,7 @@ export { retry } from './retry';
 export { retryWhen } from './retryWhen';
 export { refCount } from './refCount';
 export { sample } from './sample';
+export { sampleTime } from './sampleTime';
 export { scan } from './scan';
 export { subscribeOn } from './subscribeOn';
 export { switchAll } from './switchAll';

src/operators/sampleTime.ts

@@ -0,0 +1,94 @@
+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { IScheduler } from '../Scheduler';
+import { Action } from '../scheduler/Action';
+import { async } from '../scheduler/async';
+import { TeardownLogic } from '../Subscription';
+
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * 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<T>(period: number, scheduler: IScheduler = async): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new SampleTimeOperator(period, scheduler));
+}
+
+class SampleTimeOperator<T> implements Operator<T, T> {
+  constructor(private period: number,
+              private scheduler: IScheduler) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new SampleTimeSubscriber(subscriber, this.period, this.scheduler));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class SampleTimeSubscriber<T> extends Subscriber<T> {
+  lastValue: T;
+  hasValue: boolean = false;
+
+  constructor(destination: Subscriber<T>,
+              private period: number,
+              private scheduler: IScheduler) {
+    super(destination);
+    this.add(scheduler.schedule(dispatchNotification, period, { subscriber: this, period }));
+  }
+
+  protected _next(value: T) {
+    this.lastValue = value;
+    this.hasValue = true;
+  }
+
+  notifyNext() {
+    if (this.hasValue) {
+      this.hasValue = false;
+      this.destination.next(this.lastValue);
+    }
+  }
+}
+
+function dispatchNotification<T>(this: Action<any>, state: any) {
+  let { subscriber, period } = state;
+  subscriber.notifyNext();
+  this.schedule(state, period);
+}