Filter all 'null' values from an Observable<T>

Question

I have a service with a subject:

@Injectable() export class UserService() {
    private currentUserSubject = new BehaviorSubject<User>(null);
    public currentUser = this.currentUserSubject.asObservable().distinctUntilChanged(); 

    ... // emitting new User    
}

Have a component I inject this service into and subscribing on updates:

@Component() export class UserComponent {
    constructor(private userService: UserService) {
        this.userService.currentUser
            .subscribe((user) => {
                // I want to see not null value here
            })
    }
}

I want to apply something to Observable<User> to filter all null values and get into subscribe only when User is actually loaded.

Answer 1

Add a filter operator to your observable chain. You can filter nulls explicitly or just check that your user is truthy - you will have to make that call depending on your needs.

Filtering out null users only:

public currentUser = this.currentUserSubject
                         .asObservable()
                         .filter(user => user !== null)
                         .distinctUntilChanged();