How to block a subscription call in constructor until completed?

Question

How may I block a constructor, to wait for an Http call to return data?

constructor() {
  this.initRestData().subscribe();
  // wait for data to be read
  this.nextStep();
}

The data retreived by the initRestData() call is needed by other services/components in the application. I only have to do this at startup. If there is a better way to handle this then Observable that would be ok too.

Answer 1

You could chain the calls either inside the subscribe or in a do -operator:

constructor() {
  this.initRestData()
    .do(receivedData => this.nextStep(receivedData)})
    .subscribe();
}

---

For the case that other services rely on this.nextStep() as well, you should implement this as a stream as well:

private initialData$ = new BehaviorSubject<any>(null);
constructor() {
  this.initRestData()
    .do(data => this.initialData$.next(data))
    .switchMap(() => this.nextStep())
    .subscribe();
}

nextStep(): Observable<any> {
    return this.initialData$
        .filter(data => data != null)
        .take(1)
        .map(data => {
            // do the logic of "nextStep"
            // and return the result
        });
}