How to know which observable triggers change in Rx.Observable.combineLatest

Question

I can use Rx.Observable.combineLatest so that I will notify the changes whenever any observable changes. But how can I know which observable changes?

var s1 = someObservable1();
var s2 = someObservable2();
Rx.Observable.combineLatest(s1, s2).subscribe(function(){
    // How to know which Observable triggers combineLatest change

});

score 11 · Answer 1 · answered Jan 11 '17 at 07:36

11

RxJs provides no means to accomplish this. Nevertheless you can do it with additional state:

var trigger = "";

Rx.Observable
  .combineLatest(
    s1.do(function() { trigger = "s1"; }),
    s2.do(function() { trigger = "s2"; }))
  .subscribe(function(){
    // use trigger
  });

answered Jan 11 '17 at 07:36

Sergey Sokolov

2,709
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31

2

looks so dirty, since we store state outside of the pipeline. Doesn't look good. But definitely works – denis631 Oct 02 '18 at 10:01
4

making a tuple (item, timestamp) and combining them together than taking the item which has greater timestamp as last event works as well. Having external variable doesn't seem like right approach – denis631 Oct 02 '18 at 10:52
1

I agree with @denis631. In fact, it seems that many RX implementation have a `Timestamp()` operator built in. https://reactivex.io/documentation/operators/timestamp.html#:~:text=RxJS%20timestamp,emitted%20by%20the%20source%20Observable. – freakTheMighty May 03 '22 at 14:06

How to know which observable triggers change in Rx.Observable.combineLatest

1 Answers1