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

src/operator/skipWhile.ts

@@ -1,7 +1,5 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { TeardownLogic } from '../Subscription';
+import { skipWhile as higherOrder } from '../operators/skipWhile';
 
 /**
  * Returns an Observable that skips all items emitted by the source Observable as long as a specified condition holds
@@ -16,49 +14,5 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 export function skipWhile<T>(this: Observable<T>, predicate: (value: T, index: number) => boolean): Observable<T> {
-  return this.lift(new SkipWhileOperator(predicate));
-}
-
-class SkipWhileOperator<T> implements Operator<T, T> {
-  constructor(private predicate: (value: T, index: number) => boolean) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new SkipWhileSubscriber(subscriber, this.predicate));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class SkipWhileSubscriber<T> extends Subscriber<T> {
-  private skipping: boolean = true;
-  private index: number = 0;
-
-  constructor(destination: Subscriber<T>,
-              private predicate: (value: T, index: number) => boolean) {
-    super(destination);
-  }
-
-  protected _next(value: T): void {
-    const destination = this.destination;
-    if (this.skipping) {
-      this.tryCallPredicate(value);
-    }
-
-    if (!this.skipping) {
-      destination.next(value);
-    }
-  }
-
-  private tryCallPredicate(value: T): void {
-    try {
-      const result = this.predicate(value, this.index++);
-      this.skipping = Boolean(result);
-    } catch (err) {
-      this.destination.error(err);
-    }
-  }
+  return higherOrder(predicate)(this);
 }

src/operators/index.ts

@@ -63,6 +63,7 @@ export { scan } from './scan';
 export { skip } from './skip';
 export { skipLast } from './skipLast';
 export { skipUntil } from './skipUntil';
+export { skipWhile } from './skipWhile';
 export { subscribeOn } from './subscribeOn';
 export { switchAll } from './switchAll';
 export { switchMap } from './switchMap';

src/operators/skipWhile.ts

@@ -0,0 +1,65 @@
+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { TeardownLogic } from '../Subscription';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Returns an Observable that skips all items emitted by the source Observable as long as a specified condition holds
+ * true, but emits all further source items as soon as the condition becomes false.
+ *
+ * <img src="./img/skipWhile.png" width="100%">
+ *
+ * @param {Function} predicate - A function to test each item emitted from the source Observable.
+ * @return {Observable<T>} An Observable that begins emitting items emitted by the source Observable when the
+ * specified predicate becomes false.
+ * @method skipWhile
+ * @owner Observable
+ */
+export function skipWhile<T>(predicate: (value: T, index: number) => boolean): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new SkipWhileOperator(predicate));
+}
+
+class SkipWhileOperator<T> implements Operator<T, T> {
+  constructor(private predicate: (value: T, index: number) => boolean) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new SkipWhileSubscriber(subscriber, this.predicate));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class SkipWhileSubscriber<T> extends Subscriber<T> {
+  private skipping: boolean = true;
+  private index: number = 0;
+
+  constructor(destination: Subscriber<T>,
+              private predicate: (value: T, index: number) => boolean) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    const destination = this.destination;
+    if (this.skipping) {
+      this.tryCallPredicate(value);
+    }
+
+    if (!this.skipping) {
+      destination.next(value);
+    }
+  }
+
+  private tryCallPredicate(value: T): void {
+    try {
+      const result = this.predicate(value, this.index++);
+      this.skipping = Boolean(result);
+    } catch (err) {
+      this.destination.error(err);
+    }
+  }
+}