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

Author: jasonaden

src/operator/skip.ts

@@ -1,7 +1,5 @@
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
 import { Observable } from '../Observable';
-import { TeardownLogic } from '../Subscription';
+import { skip as higherOrder } from '../operators/skip';
 
 /**
  * Returns an Observable that skips the first `count` items emitted by the source Observable.
@@ -15,33 +13,5 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 export function skip<T>(this: Observable<T>, count: number): Observable<T> {
-  return this.lift(new SkipOperator(count));
-}
-
-class SkipOperator<T> implements Operator<T, T> {
-  constructor(private total: number) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new SkipSubscriber(subscriber, this.total));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class SkipSubscriber<T> extends Subscriber<T> {
-  count: number = 0;
-
-  constructor(destination: Subscriber<T>, private total: number) {
-    super(destination);
-  }
-
-  protected _next(x: T) {
-    if (++this.count > this.total) {
-      this.destination.next(x);
-    }
-  }
+  return higherOrder(count)(this);
 }

src/operators/index.ts

@@ -60,6 +60,7 @@ export { race } from './race';
 export { reduce } from './reduce';
 export { refCount } from './refCount';
 export { scan } from './scan';
+export { skip } from './skip';
 export { subscribeOn } from './subscribeOn';
 export { switchAll } from './switchAll';
 export { switchMap } from './switchMap';

src/operators/skip.ts

@@ -0,0 +1,48 @@
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Observable } from '../Observable';
+import { TeardownLogic } from '../Subscription';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Returns an Observable that skips the first `count` items emitted by the source Observable.
+ *
+ * <img src="./img/skip.png" width="100%">
+ *
+ * @param {Number} count - The number of times, items emitted by source Observable should be skipped.
+ * @return {Observable} An Observable that skips values emitted by the source Observable.
+ *
+ * @method skip
+ * @owner Observable
+ */
+export function skip<T>(count: number): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new SkipOperator(count));
+}
+
+class SkipOperator<T> implements Operator<T, T> {
+  constructor(private total: number) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new SkipSubscriber(subscriber, this.total));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class SkipSubscriber<T> extends Subscriber<T> {
+  count: number = 0;
+
+  constructor(destination: Subscriber<T>, private total: number) {
+    super(destination);
+  }
+
+  protected _next(x: T) {
+    if (++this.count > this.total) {
+      this.destination.next(x);
+    }
+  }
+}