[RxJS] Replace zip with combineLatest when combining sources of data

This lesson will highlight the true purpose of the zip operator, and how uncommon its use cases are. In its place, we will learn how to use the combineLatest operator.

const length$ = Rx.Observable.of(5, 4);
const width$ = Rx.Observable.of(7,1);
const height$ = Rx.Observable.of(2.8, 2.5);

const volume$ = Rx.Observable
  .zip(length$, width$, height$,
    (length, width, height) => length * width * height
  );

volume$.subscribe(function (volume) {
  console.log(volume);
});

zip requiers each observable has synchronized emissions.  It means:

const length$ = Rx.Observable.of(5);
const width$ = Rx.Observable.of(7);
const height$ = Rx.Observable.of(2.8, 2.5);

2.5 won‘t be calculated only when lenth$ and width$ provide second value.

In this case we can use combineLatest instead of zip:

const length$ = Rx.Observable.of(5);
const width$ = Rx.Observable.of(7);
const height$ = Rx.Observable.of(2.8, 2.5);

const volume$ = Rx.Observable
  .combineLatest(length$, width$, height$,
    (length, width, height) => length * width * height
  );

volume$.subscribe(function (volume) {
  console.log(volume);
});