Return Observable<boolean> from service method after two subscriptions resolve

Question

I'm trying to setup a simple way to compare the current username with a profile's username within an Angular service.

Obviously the profile username and the user's username must resolve before I can compare them so how do I return a boolean observable so that I can subscribe to this comparison within components?

This is where I'm at:

public profileId = new Subject<string>; // Observable string source updated from a profile.component (when the URL displays the profile's username)
public profileId$ = this.profileId.asObservable();
public currentUser = this.principal.asObservable().distinctUntilChanged();

public isProfileOwner(): Observable<boolean> { // A function whose declared type is neither 'void' nor 'any' must return a value.
    this.currentUser.subscribe(user => {
            this.profileId$.subscribe(
                profile => {
                    console.log(profile + ' ' + user.username); // match!
                    if (profile === user.username) {
                        return Observable.of(true);
                    } else {
                        return Observable.of(false);
                    }
                }
            )
        })
}

This seems to be the way other SO answers explain to do it but I'm getting [ts] A function whose declared type is neither 'void' nor 'any' must return a value.

I'd like to subscribe to test within components.

this.authService.isProfileOwner().subscribe(
    data => {
        console.log(data); // should be boolean
    }
)

Answer 1

As noticed from other answer by @user184994, forkJoin won't work in this case. Instead you can use combineLatest, and then very similarily like @user184994 have otherwise implemented the service code:

isProfileOwner(): Observable<boolean> {
  return Observable.combineLatest(this.currentUser, this.profileId$)
    .map(results => {
       let user = results[0];
       let profile = results[1];
       return (user.username === profile)
    });
}

DEMO