epics5.js

const applyForce = (action$, store) =>
  action$.ofType(actions.APPLY_FORCE_CLICK)
    .throttleTime(100)
    // Do not apply force unless game is ongoing.
    .filter(_action => selectors.isGameOngoing(store.getState()))
    .map(action => actions.applyForce(action.payload));

const game = (action$, store) =>
  action$.ofType(actions.START_CLICK)
    // Do not start game if it is already ongoing.
    .filter(action => !selectors.isGameOngoing(store.getState()))
    .mergeMap(() => {
      const start = Observable.of(actions.start());
      const interval = Observable.interval(250)
        .takeUntil(action$.ofType(
          actions.PAUSE,
          actions.RESET,
          actions.END
        ));
      const incrementTime = interval
        .map(_interval => actions.incrementTime());
      const end = interval
        // Only end game if the user has lost.
        .filter(_action => selectors.shouldGameEnd(store.getState()))
        .map(_action => actions.end());
      return Observable.merge(start, incrementTime, end);
    });