feat(finalize): add higher-order lettable version of finally, called …

…finalize

src/operator/finally.ts

@@ -1,7 +1,6 @@
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { Subscription, TeardownLogic } from '../Subscription';
+
 import { Observable } from '../Observable';
+import { finalize } from '../operators';
 
 /**
  * Returns an Observable that mirrors the source Observable, but will call a specified function when
@@ -12,26 +11,5 @@ import { Observable } from '../Observable';
  * @owner Observable
  */
 export function _finally<T>(this: Observable<T>, callback: () => void): Observable<T> {
-  return this.lift(new FinallyOperator(callback));
-}
-
-class FinallyOperator<T> implements Operator<T, T> {
-  constructor(private callback: () => void) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new FinallySubscriber(subscriber, this.callback));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class FinallySubscriber<T> extends Subscriber<T> {
-  constructor(destination: Subscriber<T>, callback: () => void) {
-    super(destination);
-    this.add(new Subscription(callback));
-  }
+  return finalize(callback)(this);
 }

src/operators/finalize.ts

@@ -0,0 +1,38 @@
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Subscription, TeardownLogic } from '../Subscription';
+import { Observable } from '../Observable';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Returns an Observable that mirrors the source Observable, but will call a specified function when
+ * the source terminates on complete or error.
+ * @param {function} callback Function to be called when source terminates.
+ * @return {Observable} An Observable that mirrors the source, but will call the specified function on termination.
+ * @method finally
+ * @owner Observable
+ */
+export function finalize<T>(callback: () => void): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new FinallyOperator(callback));
+}
+
+class FinallyOperator<T> implements Operator<T, T> {
+  constructor(private callback: () => void) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new FinallySubscriber(subscriber, this.callback));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class FinallySubscriber<T> extends Subscriber<T> {
+  constructor(destination: Subscriber<T>, callback: () => void) {
+    super(destination);
+    this.add(new Subscription(callback));
+  }
+}

src/operators/index.ts

@@ -25,6 +25,7 @@ export { exhaust } from './exhaust';
 export { exhaustMap } from './exhaustMap';
 export { expand } from './expand';
 export { filter } from './filter';
+export { finalize } from './finalize';
 export { ignoreElements } from './ignoreElements';
 export { map } from './map';
 export { materialize } from './materialize';