javascript - ForkJoin 2 BehaviorSubjects

Question

I have two behaviour subject streams what I'm trying to forkJoin with no luck. As I imagined it gives back the two last values of it. Is this possible to implement it somehow?

It is not called after the subject.

let stream1 = new BehaviorSubject(2);
let stream2 = new BehaviorSubject('two');

Observable.forkJoin(stream1, stream2)
    .subscribe(r => {
         console.log(r);
    });

Answer 1

Note what forkJoin() actually does from its documentation:

Wait for Observables to complete and then combine last values they emitted.

This means that forkJoin() emits a value when all input Observable are complete. When using BehaviorSubject this means explicitly calling complete() on both of them:

import { Observable, BehaviorSubject, forkJoin } from 'rxjs';

const stream1 = new BehaviorSubject(2);
const stream2 = new BehaviorSubject('two');

forkJoin(stream1, stream2)
  .subscribe(r => {
    console.log(r);
  });

stream1.complete();
stream2.complete();

See live demo: https://stackblitz.com/edit/rxjs-9nqtx6

March 2019: Updated for RxJS 6.