Observable.forkJoin() doesn't execute

Question

I have the following code:

//Loop: For each user ID/Role ID, get the data userMeta.forEach((businessRole) => {   Observable.forkJoin(     af.database.object('/roles/'+businessRole.$value),     af.database.object('/users/'+businessRole.$key)   ).subscribe(     data => {       console.log("Data received");       data[1].role = data[0];       this.users.push(data[1]);     },     err => console.error(err)   ); 

I am trying to subscribe to a result of 2 observables using forkJoin.

For some reasons, the "Data received" message is not shown.

My userMeta variables looks fine at console.log:

What's wrong?

Update: the following code does not return anything either

let source = Observable.forkJoin(         af.database.object('/roles/'+businessRole.$value),         af.database.object('/users/'+businessRole.$key)     );     let subscription = source.subscribe(       function (x) {     console.log("GOT: " + x);   },   function (err) {     console.log('Error: %s', err);   },   function () {     console.log('Completed');   }); 

What I actually trying to do is improve the performance of the following code:

//Subscription 3: role ID to role Name         af.database.object('/roles/'+businessRole.$value)         .subscribe((roleData) => {         //Subscription 4: Get user info         af.database.object('/users/'+businessRole.$key).subscribe(user => { 

Answer 1

forkJoin() requires all source Observables to emit at least once and to complete.

This following demo completes as expected:

const source = forkJoin(   from([1,2,3]),   from([9,8,7,6]) ).subscribe(   x => console.log('GOT:', x),   err => console.log('Error:', err),   () => console.log('Completed') ); 

Live demo: https://stackblitz.com/edit/rxjs-urhkni

GOT: 3,6 Completed 

Jan 2019: Updated for RxJS 6