What is the process for subscribing when setting up an observable?

There's this situation where I have an observable that emits an ID. My goal is to fetch an element associated with that ID and save it into a new observable. The catch is, the new observable must be subscribed to in order to emit its value. Here's how the code currently looks:

selectedElement$ =
  latestElementId$.pipe(
    takeUntil(this.destroy$),
    mergeMap(id => store$.select(selectElement(id))),
    tap(element => elementForm?.patchValue(element))
  );
selectedElement$
  .pipe(takeUntil(this.destroy$))
  .subscribe();

I can't shake off this feeling that there might be a more efficient way to handle this scenario, perhaps utilizing another operator that could eliminate the need for the last three lines. However, when I attempted to remove them, the code stopped functioning properly.

Answer №1

I'm not entirely sure about the purpose of repeatedly using tap to output an observable, but here's how I would have approached writing this piece of code:

// Initialize our observables
latestElementId$ = new BehaviorSubject<any>(23);
selectedElement$ = new BehaviorSubject<any>(null);

// Subscribe to latestElementId$
latestElementId$
  .asObservable()
  .pipe(
    // Ensure that the code only runs when the value changes
    distinctUntilChanged(),
    // Perform desired actions here
    mergeMap(id => store$.select(selectElement(id)))
  )
  .subscribe((element: any) => {
    // Update the form with the element value
    elementForm?.patchValue(element);

    // Notify subscribers by updating selectedElement observable
    selectedElement$.next(element);
  });

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