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

src/operator/bufferWhen.ts

@@ -1,13 +1,6 @@
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { Observable } from '../Observable';
-import { Subscription } from '../Subscription';
-import { tryCatch } from '../util/tryCatch';
-import { errorObject } from '../util/errorObject';
 
-import { OuterSubscriber } from '../OuterSubscriber';
-import { InnerSubscriber } from '../InnerSubscriber';
-import { subscribeToResult } from '../util/subscribeToResult';
+import { Observable } from '../Observable';
+import { bufferWhen as higherOrder } from '../operators';
 
 /**
  * Buffers the source Observable values, using a factory function of closing
@@ -43,92 +36,5 @@ import { subscribeToResult } from '../util/subscribeToResult';
  * @owner Observable
  */
 export function bufferWhen<T>(this: Observable<T>, closingSelector: () => Observable<any>): Observable<T[]> {
-  return this.lift(new BufferWhenOperator<T>(closingSelector));
-}
-
-class BufferWhenOperator<T> implements Operator<T, T[]> {
-
-  constructor(private closingSelector: () => Observable<any>) {
-  }
-
-  call(subscriber: Subscriber<T[]>, source: any): any {
-    return source.subscribe(new BufferWhenSubscriber(subscriber, this.closingSelector));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class BufferWhenSubscriber<T> extends OuterSubscriber<T, any> {
-  private buffer: T[];
-  private subscribing: boolean = false;
-  private closingSubscription: Subscription;
-
-  constructor(destination: Subscriber<T[]>, private closingSelector: () => Observable<any>) {
-    super(destination);
-    this.openBuffer();
-  }
-
-  protected _next(value: T) {
-    this.buffer.push(value);
-  }
-
-  protected _complete() {
-    const buffer = this.buffer;
-    if (buffer) {
-      this.destination.next(buffer);
-    }
-    super._complete();
-  }
-
-  protected _unsubscribe() {
-    this.buffer = null;
-    this.subscribing = false;
-  }
-
-  notifyNext(outerValue: T, innerValue: any,
-             outerIndex: number, innerIndex: number,
-             innerSub: InnerSubscriber<T, any>): void {
-    this.openBuffer();
-  }
-
-  notifyComplete(): void {
-    if (this.subscribing) {
-      this.complete();
-    } else {
-      this.openBuffer();
-    }
-  }
-
-  openBuffer() {
-
-    let { closingSubscription } = this;
-
-    if (closingSubscription) {
-      this.remove(closingSubscription);
-      closingSubscription.unsubscribe();
-    }
-
-    const buffer = this.buffer;
-    if (this.buffer) {
-      this.destination.next(buffer);
-    }
-
-    this.buffer = [];
-
-    const closingNotifier = tryCatch(this.closingSelector)();
-
-    if (closingNotifier === errorObject) {
-      this.error(errorObject.e);
-    } else {
-      closingSubscription = new Subscription();
-      this.closingSubscription = closingSubscription;
-      this.add(closingSubscription);
-      this.subscribing = true;
-      closingSubscription.add(subscribeToResult(this, closingNotifier));
-      this.subscribing = false;
-    }
-  }
+  return higherOrder(closingSelector)(this);
 }

src/operators/bufferWhen.ts

@@ -0,0 +1,136 @@
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Observable } from '../Observable';
+import { Subscription } from '../Subscription';
+import { tryCatch } from '../util/tryCatch';
+import { errorObject } from '../util/errorObject';
+import { OuterSubscriber } from '../OuterSubscriber';
+import { InnerSubscriber } from '../InnerSubscriber';
+import { subscribeToResult } from '../util/subscribeToResult';
+import { OperatorFunction } from '../interfaces';
+
+/**
+ * Buffers the source Observable values, using a factory function of closing
+ * Observables to determine when to close, emit, and reset the buffer.
+ *
+ * <span class="informal">Collects values from the past as an array. When it
+ * starts collecting values, it calls a function that returns an Observable that
+ * tells when to close the buffer and restart collecting.</span>
+ *
+ * <img src="./img/bufferWhen.png" width="100%">
+ *
+ * Opens a buffer immediately, then closes the buffer when the observable
+ * returned by calling `closingSelector` function emits a value. When it closes
+ * the buffer, it immediately opens a new buffer and repeats the process.
+ *
+ * @example <caption>Emit an array of the last clicks every [1-5] random seconds</caption>
+ * var clicks = Rx.Observable.fromEvent(document, 'click');
+ * var buffered = clicks.bufferWhen(() =>
+ *   Rx.Observable.interval(1000 + Math.random() * 4000)
+ * );
+ * buffered.subscribe(x => console.log(x));
+ *
+ * @see {@link buffer}
+ * @see {@link bufferCount}
+ * @see {@link bufferTime}
+ * @see {@link bufferToggle}
+ * @see {@link windowWhen}
+ *
+ * @param {function(): Observable} closingSelector A function that takes no
+ * arguments and returns an Observable that signals buffer closure.
+ * @return {Observable<T[]>} An observable of arrays of buffered values.
+ * @method bufferWhen
+ * @owner Observable
+ */
+export function bufferWhen<T>(closingSelector: () => Observable<any>): OperatorFunction<T, T[]> {
+  return function (source: Observable<T>) {
+    return source.lift(new BufferWhenOperator(closingSelector));
+  };
+}
+
+class BufferWhenOperator<T> implements Operator<T, T[]> {
+
+  constructor(private closingSelector: () => Observable<any>) {
+  }
+
+  call(subscriber: Subscriber<T[]>, source: any): any {
+    return source.subscribe(new BufferWhenSubscriber(subscriber, this.closingSelector));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class BufferWhenSubscriber<T> extends OuterSubscriber<T, any> {
+  private buffer: T[];
+  private subscribing: boolean = false;
+  private closingSubscription: Subscription;
+
+  constructor(destination: Subscriber<T[]>, private closingSelector: () => Observable<any>) {
+    super(destination);
+    this.openBuffer();
+  }
+
+  protected _next(value: T) {
+    this.buffer.push(value);
+  }
+
+  protected _complete() {
+    const buffer = this.buffer;
+    if (buffer) {
+      this.destination.next(buffer);
+    }
+    super._complete();
+  }
+
+  protected _unsubscribe() {
+    this.buffer = null;
+    this.subscribing = false;
+  }
+
+  notifyNext(outerValue: T, innerValue: any,
+             outerIndex: number, innerIndex: number,
+             innerSub: InnerSubscriber<T, any>): void {
+    this.openBuffer();
+  }
+
+  notifyComplete(): void {
+    if (this.subscribing) {
+      this.complete();
+    } else {
+      this.openBuffer();
+    }
+  }
+
+  openBuffer() {
+
+    let { closingSubscription } = this;
+
+    if (closingSubscription) {
+      this.remove(closingSubscription);
+      closingSubscription.unsubscribe();
+    }
+
+    const buffer = this.buffer;
+    if (this.buffer) {
+      this.destination.next(buffer);
+    }
+
+    this.buffer = [];
+
+    const closingNotifier = tryCatch(this.closingSelector)();
+
+    if (closingNotifier === errorObject) {
+      this.error(errorObject.e);
+    } else {
+      closingSubscription = new Subscription();
+      this.closingSubscription = closingSubscription;
+      this.add(closingSubscription);
+      this.subscribing = true;
+      closingSubscription.add(subscribeToResult(this, closingNotifier));
+      this.subscribing = false;
+    }
+  }
+}

src/operators/index.ts

@@ -4,6 +4,7 @@ export { buffer } from './buffer';
 export { bufferCount } from './bufferCount';
 export { bufferTime } from './bufferTime';
 export { bufferToggle } from './bufferToggle';
+export { bufferWhen } from './bufferWhen';
 export { catchError } from './catchError';
 export { concat } from './concat';
 export { concatAll } from './concatAll';