feat(throttle): add throttle operator with durationSelector

Add new throttle operator (previous throttle was renamed to throttleTime) that takes a
durationSelector parameter, much like debounce does.

Resolves #496.

src/CoreOperators.ts

@@ -75,6 +75,7 @@ export interface CoreOperators<T> {
   switchMapTo?: <R>(observable: Observable<any>, projectResult?: (x: T, y: any, ix: number, iy: number) => R) => Observable<R>;
   take?: (count: number) => Observable<T>;
   takeUntil?: (notifier: Observable<any>) => Observable<T>;
+  throttle?: (durationSelector: (value: T) => Observable<any> | Promise<any>) => Observable<T>;
   throttleTime?: (delay: number, scheduler?: Scheduler) => Observable<T>;
   timeout?: (due: number | Date, errorToSend?: any, scheduler?: Scheduler) => Observable<T>;
   timeoutWith?: <R>(due: number | Date, withObservable: Observable<R>, scheduler?: Scheduler) => Observable<T> | Observable<R>;

src/Observable.ts

@@ -228,6 +228,7 @@ export class Observable<T> implements CoreOperators<T>  {
   switchMapTo: <R>(observable: Observable<any>, projectResult?: (x: T, y: any, ix: number, iy: number) => R) => Observable<R>;
   take: (count: number) => Observable<T>;
   takeUntil: (notifier: Observable<any>) => Observable<T>;
+  throttle: (durationSelector: (value: T) => Observable<any> | Promise<any>) => Observable<T>;
   throttleTime: (delay: number, scheduler?: Scheduler) => Observable<T>;
   timeout: (due: number | Date, errorToSend?: any, scheduler?: Scheduler) => Observable<T>;
   timeoutWith: <R>(due: number | Date, withObservable: Observable<R>, scheduler?: Scheduler) => Observable<T> | Observable<R>;

src/Rx.KitchenSink.ts

@@ -285,6 +285,9 @@ observableProto.take = take;
 import {takeUntil} from './operators/takeUntil';
 observableProto.takeUntil = takeUntil;
 
+import {throttle} from './operators/throttle';
+observableProto.throttle = throttle;
+
 import {throttleTime} from './operators/throttleTime';
 observableProto.throttleTime = throttleTime;
 

src/Rx.ts

@@ -239,6 +239,9 @@ observableProto.take = take;
 import {takeUntil} from './operators/takeUntil';
 observableProto.takeUntil = takeUntil;
 
+import {throttle} from './operators/throttle';
+observableProto.throttle = throttle;
+
 import {throttleTime} from './operators/throttleTime';
 observableProto.throttleTime = throttleTime;
 

src/operators/throttle.ts

@@ -0,0 +1,84 @@
+import {Operator} from '../Operator';
+import {Observable} from '../Observable';
+import {PromiseObservable} from '../observables/PromiseObservable';
+import {Subscriber} from '../Subscriber';
+import {Subscription} from '../Subscription';
+
+import {tryCatch} from '../util/tryCatch';
+import {isPromise} from '../util/isPromise';
+import {errorObject} from '../util/errorObject';
+
+export function throttle<T>(durationSelector: (value: T) => Observable<any> | Promise<any>): Observable<T> {
+  return this.lift(new ThrottleOperator(durationSelector));
+}
+
+class ThrottleOperator<T, R> implements Operator<T, R> {
+  constructor(private durationSelector: (value: T) => Observable<any> | Promise<any>) {
+  }
+
+  call(subscriber: Subscriber<T>): Subscriber<T> {
+    return new ThrottleSubscriber(subscriber, this.durationSelector);
+  }
+}
+
+class ThrottleSubscriber<T> extends Subscriber<T> {
+  private throttled: Subscription<any>;
+
+  constructor(destination: Subscriber<T>,
+              private durationSelector: (value: T) => Observable<any> | Promise<any>) {
+    super(destination);
+  }
+
+  _next(value: T): void {
+    if (!this.throttled) {
+      const destination = this.destination;
+      let duration = tryCatch(this.durationSelector)(value);
+      if (duration === errorObject) {
+        destination.error(errorObject.e);
+        return;
+      }
+      if (isPromise(duration)) {
+        duration = PromiseObservable.create(duration);
+      }
+      this.add(this.throttled = duration._subscribe(new ThrottleDurationSelectorSubscriber(this)));
+      destination.next(value);
+    }
+  }
+
+  _error(err: any): void {
+    this.clearThrottle();
+    super._error(err);
+  }
+
+  _complete(): void {
+    this.clearThrottle();
+    super._complete();
+  }
+
+  clearThrottle(): void {
+    const throttled = this.throttled;
+    if (throttled) {
+      throttled.unsubscribe();
+      this.remove(throttled);
+      this.throttled = null;
+    }
+  }
+}
+
+class ThrottleDurationSelectorSubscriber<T> extends Subscriber<T> {
+  constructor(private parent: ThrottleSubscriber<any>) {
+    super(null);
+  }
+
+  _next(unused: T): void {
+    this.parent.clearThrottle();
+  }
+
+  _error(err): void {
+    this.parent.error(err);
+  }
+
+  _complete(): void {
+    this.parent.clearThrottle();
+  }
+}