1. override
dynamic call(Store<State, Action> store, Action action, NextDispatcher next)

Source

@override
call(Store<State, Action> store, Action action, NextDispatcher next) {
  if (!isSubscribed) {
    observable(epics.stream)
        .flatMapLatest(
            (epic) => epic.map(actions.stream, new EpicStore(store)))
        .listen((action) => next(action));

    epics.add(epic);

    isSubscribed = true;
  }

  next(action);
  actions.add(action);
}