How do I force a refresh on an Observable service in Angular2?

In order for an observable to be able to provide values after initial Http observable was completed, it can be provided by RxJS subject. Since caching behaviour is desirable, ReplaySubject fits the case.

It should be something like

class UserService {
  private usersSubject: Subject;
  private usersRequest: Observable;
  private usersSubscription: Subscription;

  constructor(private http: Http) {
    this.usersSubject = new ReplaySubject(1);
  }

  getUsers(refresh: boolean = false) {
    if (refresh || !this.usersRequest) {
      this.usersRequest = this.http.get(...).map(res => res.json().result);

      this.usersRequest.subscribe(
        result => this.usersSubject.next(result),
        err => this.usersSubject.error(err)
      );
    }

    return this.usersSubject.asObservable();
  }
  onDestroy() {
    this.usersSubscription.unsubscribe();
  }
}

Since the subject already exists, a new user can be pushed without updating the list from server:

this.getUsers().take(1).subscribe(users => 
  this.usersSubject.next([...users, newUser])
)