Angular 2 rxjs observables created from BehaviorSubject are not working with forkJoin

Question

I am trying to use Observable.forkJoin and the subscribe handler is never getting hit. The forkJoin operator is working for me in other parts of my app and the only difference I can think of in the non-working scenario is that the observables are being created from BehaviorSubject objects using its asObservable() function.

This subscribe gets hit

    let obs = Observable.of(1);

    Observable.forkJoin(
        obs
    ).subscribe(data => {
        console.log(data);
    });

This one does not

    let bs = new BehaviorSubject<number>(1);
    let obs = bs.asObservable();

    Observable.forkJoin(
        obs
    ).subscribe(data => {
        console.log(data);
    });

Of course in my real use case there is more than one obseravble which is why I'm using forkJoin in the first place.

Is there something else that needs to be done to BehaviorSubject to make it work with forkJoin?

UPDATE:

After investigating the RxJs docs a bit more I realized that the Observable.combineLatest was much better suited to my need than forkJoin... Link here in case any comes across this SO post: http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#static-method-combineLatest

Answer 1

The issue is that forkJoin joins the observables when they complete.

In your first snippet, you are creating an observable using of - which, upon subscribe, immediately emits a value and then completes.

In your second snippet, the BehaviorSubject does not complete. If you were to call complete, you would see the value logged to the console:

let bs = new BehaviorSubject<number>(1);
let obs = bs.asObservable();

Observable.forkJoin(
    obs
).subscribe(data => {
    console.log(data);
});

bs.complete();