CODEWITHSUNDEEP
javascriptrxjs
Iter Ator
Iter Ator

Reputation: 9289

forkJoin.subscribe with ReplaySubject is not called

I would like to create an Observable, which fires if both ReplaySubject instances are holding a value. I tried it like this:

let v1 = new Rx.ReplaySubject();
let v2 = new Rx.ReplaySubject();

v1.next('X');

const combo = Rx.Observable.forkJoin(v1, v2)

combo.subscribe( arr => console.log(arr) )

v1.subscribe( s => console.log('v1', s) );
v2.subscribe( s => console.log('v2', s) );

v2.next('Y');

Both v1.subscribe and v2.subscribe is called, but not combo.subscribe. What do I wrong? How is it possible to fix this issue?

Upvotes: 2

Views: 1355

Answers (2)

JJWesterkamp
JJWesterkamp

Reputation: 7916

forkJoin will only emit an array of all last values of the input observables once all of them complete. If you manually complete v1 and v2, combo will emit:

let v1 = new rxjs.ReplaySubject();
let v2 = new rxjs.ReplaySubject();

v1.next('X');
v2.next('Y');
v2.next('Z'); // This additional value should demonstrate the idea of forkJoin

const combo = rxjs.forkJoin(v1, v2)
combo.subscribe( arr => console.log(arr) )

v1.complete();
v2.complete();
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.2/rxjs.umd.js"></script>

You might be looking for combineLatest instead if you don't want the inner observables to complete:

let v1 = new rxjs.ReplaySubject();
let v2 = new rxjs.ReplaySubject();

v1.next('X');
v2.next('Y');

const combo = rxjs.combineLatest(v1, v2)
combo.subscribe( arr => console.log(arr) )
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.2/rxjs.umd.js"></script>

Upvotes: 5

OJ Kwon
OJ Kwon

Reputation: 4641

forkJoin waits for input observables to complete, then emit last item emitted. You have to complete both subject.

Upvotes: 2

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