feat(ignoreElements): add higher-order lettable version of ignoreElem…

…ents

src/operator/ignoreElements.ts

@@ -1,7 +1,5 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { noop } from '../util/noop';
+import { ignoreElements as higherOrder } from '../operators';
 
 /**
  * Ignores all items emitted by the source Observable and only passes calls of `complete` or `error`.
@@ -14,22 +12,5 @@ import { noop } from '../util/noop';
  * @owner Observable
  */
 export function ignoreElements<T>(this: Observable<T>): Observable<T> {
-  return this.lift(new IgnoreElementsOperator());
+  return higherOrder()(this);
 };
-
-class IgnoreElementsOperator<T, R> implements Operator<T, R> {
-  call(subscriber: Subscriber<R>, source: any): any {
-    return source.subscribe(new IgnoreElementsSubscriber(subscriber));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class IgnoreElementsSubscriber<T> extends Subscriber<T> {
-  protected _next(unused: T): void {
-    noop();
-  }
-}

src/operators/ignoreElements.ts

@@ -0,0 +1,38 @@
+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { noop } from '../util/noop';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Ignores all items emitted by the source Observable and only passes calls of `complete` or `error`.
+ *
+ * <img src="./img/ignoreElements.png" width="100%">
+ *
+ * @return {Observable} An empty Observable that only calls `complete`
+ * or `error`, based on which one is called by the source Observable.
+ * @method ignoreElements
+ * @owner Observable
+ */
+export function ignoreElements<T>(): MonoTypeOperatorFunction<T> {
+  return function ignoreElementsOperatorFunction(source: Observable<T>) {
+    return source.lift(new IgnoreElementsOperator());
+  };
+}
+
+class IgnoreElementsOperator<T, R> implements Operator<T, R> {
+  call(subscriber: Subscriber<R>, source: any): any {
+    return source.subscribe(new IgnoreElementsSubscriber(subscriber));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class IgnoreElementsSubscriber<T> extends Subscriber<T> {
+  protected _next(unused: T): void {
+    noop();
+  }
+}

src/operators/index.ts

@@ -2,6 +2,7 @@ export { catchError } from './catchError';
 export { concatMap } from './concatMap';
 export { defaultIfEmpty } from './defaultIfEmpty';
 export { filter } from './filter';
+export { ignoreElements } from './ignoreElements';
 export { map } from './map';
 export { max } from './max';
 export { mergeMap } from './mergeMap';