为什么操作员forkJoin不起作用？

Question

I'm trying to add two observable. But the console does not display anything.

var s = Rx.Observable.of(100, 200, 300);
var s1 = Rx.Observable.interval(1000);

var sub = Rx.Observable.forkJoin(s, s1)

sub.subscribe(x => console.log(x));

live example here

For the case of two synchronous observables there is no problem

Answer 1

forkJoin emits only when all its source Observables emit at least one item and all of them complete. Using Observable.of is fine. It emits all its values and completes immediately. But Observable.interval never completes on itself (you might want to chain it with take(N) for example.

var s1 = Rx.Observable.interval(1000).take(1);
// Now both source Observables complete so `forkJoin` will complete as well
var sub = Rx.Observable.forkJoin(s, s1);

Answer 2

If you look up the forkJoin() function in the official documentation you will see:

forkJoin will wait for all passed Observables to complete and then it will emit an array with last values from corresponding Observables.

If you look at the interval() function

interval returns an Observable that emits an infinite sequence of ascending integers ....

So your forkJoin works fine, it will just never console.log() anything, because the interval function doesn't end.