Firebase Universal Example

user.service.ts

@Injectable()
export class UserService {
  constructor(private db: AngularFireDatabase, private zone: NgZone) {}

  getUser(id: string | number): Observable<User> {
    const user$ = this.database.object('profiles/' + id);
    this.universalBlockUntilFirst(user$);

    return user$;
  }
    
  private universalBlockUntilFirst(obs: Observable<any>) {
    if (SERVER) {
      const task = Zone.current.scheduleMacroTask('universalBlockUntilFirst', () => { }, {}, () => { }, () => { });
      obs.first().subscribe(() => this.zone.runOutsideAngular(() => task.invoke()));
    }
  }
}