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

Author: jasonaden

src/operator/take.ts

@@ -1,9 +1,5 @@
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
-import { EmptyObservable } from '../observable/EmptyObservable';
 import { Observable } from '../Observable';
-import { TeardownLogic } from '../Subscription';
+import { take as higherOrder } from '../operators/take';
 
 /**
  * Emits only the first `count` values emitted by the source Observable.
@@ -39,46 +35,5 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 export function take<T>(this: Observable<T>, count: number): Observable<T> {
-  if (count === 0) {
-    return new EmptyObservable<T>();
-  } else {
-    return this.lift(new TakeOperator(count));
-  }
-}
-
-class TakeOperator<T> implements Operator<T, T> {
-  constructor(private total: number) {
-    if (this.total < 0) {
-      throw new ArgumentOutOfRangeError;
-    }
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new TakeSubscriber(subscriber, this.total));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class TakeSubscriber<T> extends Subscriber<T> {
-  private count: number = 0;
-
-  constructor(destination: Subscriber<T>, private total: number) {
-    super(destination);
-  }
-
-  protected _next(value: T): void {
-    const total = this.total;
-    const count = ++this.count;
-    if (count <= total) {
-      this.destination.next(value);
-      if (count === total) {
-        this.destination.complete();
-        this.unsubscribe();
-      }
-    }
-  }
+  return higherOrder(count)(this);
 }

src/operators/index.ts

@@ -69,6 +69,7 @@ export { subscribeOn } from './subscribeOn';
 export { switchAll } from './switchAll';
 export { switchMap } from './switchMap';
 export { switchMapTo } from './switchMapTo';
+export { take } from './take';
 export { takeLast } from './takeLast';
 export { tap } from './tap';
 export { timestamp } from './timestamp';

src/operators/take.ts

@@ -0,0 +1,87 @@
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
+import { EmptyObservable } from '../observable/EmptyObservable';
+import { Observable } from '../Observable';
+import { TeardownLogic } from '../Subscription';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Emits only the first `count` values emitted by the source Observable.
+ *
+ * <span class="informal">Takes the first `count` values from the source, then
+ * completes.</span>
+ *
+ * <img src="./img/take.png" width="100%">
+ *
+ * `take` returns an Observable that emits only the first `count` values emitted
+ * by the source Observable. If the source emits fewer than `count` values then
+ * all of its values are emitted. After that, it completes, regardless if the
+ * source completes.
+ *
+ * @example <caption>Take the first 5 seconds of an infinite 1-second interval Observable</caption>
+ * var interval = Rx.Observable.interval(1000);
+ * var five = interval.take(5);
+ * five.subscribe(x => console.log(x));
+ *
+ * @see {@link takeLast}
+ * @see {@link takeUntil}
+ * @see {@link takeWhile}
+ * @see {@link skip}
+ *
+ * @throws {ArgumentOutOfRangeError} When using `take(i)`, it delivers an
+ * ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0`.
+ *
+ * @param {number} count The maximum number of `next` values to emit.
+ * @return {Observable<T>} An Observable that emits only the first `count`
+ * values emitted by the source Observable, or all of the values from the source
+ * if the source emits fewer than `count` values.
+ * @method take
+ * @owner Observable
+ */
+export function take<T>(count: number): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => {
+    if (count === 0) {
+      return new EmptyObservable<T>();
+    } else {
+      return source.lift(new TakeOperator(count));
+    }
+  };
+}
+
+class TakeOperator<T> implements Operator<T, T> {
+  constructor(private total: number) {
+    if (this.total < 0) {
+      throw new ArgumentOutOfRangeError;
+    }
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new TakeSubscriber(subscriber, this.total));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class TakeSubscriber<T> extends Subscriber<T> {
+  private count: number = 0;
+
+  constructor(destination: Subscriber<T>, private total: number) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    const total = this.total;
+    const count = ++this.count;
+    if (count <= total) {
+      this.destination.next(value);
+      if (count === total) {
+        this.destination.complete();
+        this.unsubscribe();
+      }
+    }
+  }
+}