According to reactive functional paradigm

Question

I have following function:

_processCalenderSelect: function (oCalendarSelectOb, oEditButton) {
  let self = this;

  return oCalendarSelectOb
    .switchMap(function (oCalendar) {
      return oEditButton.getPressed()? Rx.Observable.of(oCalendar) : Rx.Observable.never();
    })
    .mergeMap(function (oCalendar) {
      return Rx.Observable.from(oCalendar.getSource().getSelectedDates());
    })
    .map(function (oDateRange) {
      return oDateRange.getStartDate();
    });

},

the first parameter is just an observable and the second is an object.

Look at the switchMap method, I am asking if the button is pressed or not.

My question is, do I break Reactive Functional Paradigm, when I ask for the button state inside the closure?

.switchMap(function (oCalendar) {
      return oEditButton.getPressed()? Rx.Observable.of(oCalendar) : Rx.Observable.never();
    })

Answer 1

Without knowing how your streams are triggered, this is "technically O.k.", however as you probably already guessed, you are kind of breaking the "spirit" of having pure, stateless functions by introducing a non-stream-state, the oEditButton - the stream cannot be guaranteed to have the same result with the same inputs every time, because there is some "external" state(button pressed or not).

So the "cleaner" approach would be (unsure if that works for your application) to have something like an oEditButtonClicked$-event-stream, that will trigger processing of selected dates.

oEditButtonClicked$
    .switchMapTo(oCalenderSelect$)
    .mergeMap(cal => Rx.Obserbalbe.from(cal.getSource....))

---

As a side-note, if you are not able to introduce that event-stream, you could still improve your code by using skipWhile:

return oCalendarSelectOb
    .skipWhile(() => oEditButton.getPressed())
    .mergeMap(function (oCalendar) {
      return Rx.Observable.from(oCalendar.getSource().getSelectedDates());
    })
    .map(function (oDateRange) {
      return oDateRange.getStartDate();
    });

(this does NOT resolve the initial question though, just a hint on the side)