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

Author: jasonaden

src/operator/takeUntil.ts

@@ -1,11 +1,5 @@
-import { Operator } from '../Operator';
 import { Observable } from '../Observable';
-import { Subscriber } from '../Subscriber';
-import { TeardownLogic } from '../Subscription';
-
-import { OuterSubscriber } from '../OuterSubscriber';
-import { InnerSubscriber } from '../InnerSubscriber';
-import { subscribeToResult } from '../util/subscribeToResult';
+import { takeUntil as higherOrder } from '../operators/takeUntil';
 
 /**
  * Emits the values emitted by the source Observable until a `notifier`
@@ -41,38 +35,5 @@ import { subscribeToResult } from '../util/subscribeToResult';
  * @owner Observable
  */
 export function takeUntil<T>(this: Observable<T>, notifier: Observable<any>): Observable<T> {
-  return this.lift(new TakeUntilOperator(notifier));
-}
-
-class TakeUntilOperator<T> implements Operator<T, T> {
-  constructor(private notifier: Observable<any>) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new TakeUntilSubscriber(subscriber, this.notifier));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class TakeUntilSubscriber<T, R> extends OuterSubscriber<T, R> {
-
-  constructor(destination: Subscriber<any>,
-              private notifier: Observable<any>) {
-    super(destination);
-    this.add(subscribeToResult(this, notifier));
-  }
-
-  notifyNext(outerValue: T, innerValue: R,
-             outerIndex: number, innerIndex: number,
-             innerSub: InnerSubscriber<T, R>): void {
-    this.complete();
-  }
-
-  notifyComplete(): void {
-    // noop
-  }
+  return higherOrder(notifier)(this);
 }

src/operators/index.ts

@@ -71,6 +71,7 @@ export { switchMap } from './switchMap';
 export { switchMapTo } from './switchMapTo';
 export { take } from './take';
 export { takeLast } from './takeLast';
+export { takeUntil } from './takeUntil';
 export { tap } from './tap';
 export { timestamp } from './timestamp';
 export { toArray } from './toArray';

src/operators/takeUntil.ts

@@ -0,0 +1,80 @@
+import { Operator } from '../Operator';
+import { Observable } from '../Observable';
+import { Subscriber } from '../Subscriber';
+import { TeardownLogic } from '../Subscription';
+
+import { OuterSubscriber } from '../OuterSubscriber';
+import { InnerSubscriber } from '../InnerSubscriber';
+import { subscribeToResult } from '../util/subscribeToResult';
+
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Emits the values emitted by the source Observable until a `notifier`
+ * Observable emits a value.
+ *
+ * <span class="informal">Lets values pass until a second Observable,
+ * `notifier`, emits something. Then, it completes.</span>
+ *
+ * <img src="./img/takeUntil.png" width="100%">
+ *
+ * `takeUntil` subscribes and begins mirroring the source Observable. It also
+ * monitors a second Observable, `notifier` that you provide. If the `notifier`
+ * emits a value or a complete notification, the output Observable stops
+ * mirroring the source Observable and completes.
+ *
+ * @example <caption>Tick every second until the first click happens</caption>
+ * var interval = Rx.Observable.interval(1000);
+ * var clicks = Rx.Observable.fromEvent(document, 'click');
+ * var result = interval.takeUntil(clicks);
+ * result.subscribe(x => console.log(x));
+ *
+ * @see {@link take}
+ * @see {@link takeLast}
+ * @see {@link takeWhile}
+ * @see {@link skip}
+ *
+ * @param {Observable} notifier The Observable whose first emitted value will
+ * cause the output Observable of `takeUntil` to stop emitting values from the
+ * source Observable.
+ * @return {Observable<T>} An Observable that emits the values from the source
+ * Observable until such time as `notifier` emits its first value.
+ * @method takeUntil
+ * @owner Observable
+ */
+export function takeUntil<T>(notifier: Observable<any>): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new TakeUntilOperator(notifier));
+}
+
+class TakeUntilOperator<T> implements Operator<T, T> {
+  constructor(private notifier: Observable<any>) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new TakeUntilSubscriber(subscriber, this.notifier));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class TakeUntilSubscriber<T, R> extends OuterSubscriber<T, R> {
+
+  constructor(destination: Subscriber<any>,
+              private notifier: Observable<any>) {
+    super(destination);
+    this.add(subscribeToResult(this, notifier));
+  }
+
+  notifyNext(outerValue: T, innerValue: R,
+             outerIndex: number, innerIndex: number,
+             innerSub: InnerSubscriber<T, R>): void {
+    this.complete();
+  }
+
+  notifyComplete(): void {
+    // noop
+  }
+}