fix(util/toSubscriber): Supplies the Subscriber constructor with empt…

…yObserver as destination if no

1921

spec/Observable-spec.ts

@@ -192,6 +192,60 @@ describe('Observable', () => {
       source.subscribe();
     });
 
+    it('should run unsubscription logic when an error is sent synchronously and subscribe is called with no arguments', () => {
+      let unsubscribeCalled = false;
+      const source = new Observable((subscriber: Rx.Subscriber<string>) => {
+        subscriber.error(0);
+        return () => {
+          unsubscribeCalled = true;
+        };
+      });
+
+      try {
+        source.subscribe();
+      } catch (e) {
+        // error'ing to an empty Observer re-throws, so catch and ignore it here.
+      }
+
+      expect(unsubscribeCalled).to.be.true;
+    });
+
+    it('should run unsubscription logic when an error is sent asynchronously and subscribe is called with no arguments', (done: MochaDone) => {
+      let unsubscribeCalled = false;
+      const source = new Observable((subscriber: Rx.Subscriber<string>) => {
+        const id = setInterval(() => {
+          try {
+            subscriber.error(0);
+          } catch (e) {
+            // asynchronously error'ing to an empty Observer re-throws, so catch and ignore it here.
+          }
+        }, 1);
+        return () => {
+          clearInterval(id);
+          unsubscribeCalled = true;
+        };
+      });
+
+      source.subscribe();
+
+      setTimeout(() => {
+        let err;
+        let errHappened = false;
+        try {
+          expect(unsubscribeCalled).to.be.true;
+        } catch (e) {
+          err = e;
+          errHappened = true;
+        } finally {
+          if (!errHappened) {
+            done();
+          } else {
+            done(err);
+          }
+        }
+      }, 100);
+    });
+
     it('should return a Subscription that calls the unsubscribe function returned by the subscriber', () => {
       let unsubscribeCalled = false;
 

src/util/toSubscriber.ts

@@ -1,6 +1,6 @@
-import { PartialObserver } from '../Observer';
 import { Subscriber } from '../Subscriber';
 import { $$rxSubscriber } from '../symbol/rxSubscriber';
+import { PartialObserver, empty as emptyObserver } from '../Observer';
 
 export function toSubscriber<T>(
   nextOrObserver?: PartialObserver<T> | ((value: T) => void),
@@ -18,8 +18,8 @@ export function toSubscriber<T>(
   }
 
   if (!nextOrObserver && !error && !complete) {
-    return new Subscriber();
+    return new Subscriber(emptyObserver);
   }
 
   return new Subscriber(nextOrObserver, error, complete);
-}
+}