Forkjoin with empty (or not) array of observables - rxjs

Question

I'm trying to detect when all my observables have completed. I have the following Observables:
let observables:any[] = [];
if(valid){
observables.push(new Observable((observer:any) => {
async(()=>{
observer.next();
observer.complete();
})
}))
}
if(confirmed){
observables.push(new Observable((observer:any) => {
async(()=>{
observer.next();
observer.complete();
})
}))
}
Observable.forkJoin(observables).subscribe(
data => {
console.log('all completed');
},
error => {
console.log(error);
}
);
I need to do something whenever all my functions are completed. Forkjoin seems to work when the observables array is not empty. But when the array is empty, it never gets called. How can I solve this?

Answer 1

you are missing the 3rd callback in subscribe. try this:
Rx.Observable.forkJoin([]).subscribe(
val => {
console.log('next');
},
err => {
console.log('err');
},
() => {
console.log('complete')
}
);
forkJoin on empty array completes immediately.
Updated for RxJS 6:
let rep: Observable<any>[] = [];
for (let i = 0; i < areas.length; i++) { // undetermined array length
rep.push(this.httpService.GET('/areas/' + areas[i].name)); // example observable's being pushed to array
}
if (rep !== []) {
forkJoin(rep).subscribe(({
next: value => {
console.log(value)
}
}));
}

Answer 2

Try this:
import { forkJoin, Observable, of } from 'rxjs';
export function forkJoinSafe<T = any>(array: Observable<T>[]): Observable<T[]> {
if (!array.length) {
return of([])
}
return forkJoin<T>(array);
}

Answer 3

You're missing complete callback. You can pass the third argument or pass an observer object instead of 3 arguments to make event checking more readable.
yourObservable.subscribe({
next: value => console.log(value),
error: error => console.log(error),
complete: () => console.log('complete'),
});