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');