fix(Reducer errors): log exceptions thrown from `store.dispatch` insi…

…de the middleware (#379)

Closes #263

Most often this is caused by exceptions in your reducers. Right now due to a bug in rxjs these errors can sometimes (but not always) be silently swallowed. This works around it by catching them ourselves and logging and logging them.

src/createEpicMiddleware.js

@@ -53,7 +53,13 @@ export function createEpicMiddleware(rootEpic, options = defaultOptions) {
           return output$;
         })
         ::switchMap(output$ => options.adapter.output(output$))
-        .subscribe(store.dispatch);
+        .subscribe(action => {
+          try {
+            store.dispatch(action);
+          } catch (err) {
+            console.error(err);
+          }
+        });
 
       // Setup initial root epic
       epic$.next(rootEpic);

test/createEpicMiddleware-spec.js

@@ -70,7 +70,31 @@ describe('createEpicMiddleware', () => {
     ]);
   });
 
-  it('should throw if you don\'t provide a rootEpic', () => {
+  it('should console error when reducer throw exception', () => {
+    sinon.spy(console, 'error');
+
+    const reducer = (state = [], action) => {
+      switch (action.type) {
+        case 'ACTION_1':
+          throw new Error();
+        default:
+          return state;
+      }
+    };
+    const epic = (action$, store) =>
+      mergeStatic(
+        action$.ofType('FIRE_1')::mapTo({ type: 'ACTION_1' }),
+        action$.ofType('FIRE_2')::mapTo({ type: 'ACTION_2' })
+      );
+    const middleware = createEpicMiddleware(epic);
+    const store = createStore(reducer, applyMiddleware(middleware));
+
+    store.dispatch({ type: 'FIRE_1' });
+    expect(console.error.callCount).to.equal(1);
+    console.error.restore();
+  });
+
+  it("should throw if you don't provide a rootEpic", () => {
     expect(() => {
       createEpicMiddleware();
     }).to.throw('You must provide a root Epic to createEpicMiddleware');