Catching Errors while calling an API from a NgRx effect

I'm trying to catch an error on the effect of a specific action. Everything is working fine, whether when the call succeeds or fails. However, I think the code is very verbose, and could be improved on, specially:

The catchError part, I'm returning empty() but I bieleve should be returning the SavedReplyDeleteFailed action. When doing so the whole effects breaks and does not compile, not sure on whats the best practice for handling this.
I'm relying too much on the tap and dispatch instead of returning the actions from the map/mergeMap call backs. When I do so the effects compilation breaks as well.

How I can apply the above improvements?

    deleteSavedReply = createEffect(() => this.actions$.pipe(
        ofType(SavedRepliesActions.SavedReplyDeleteRequested),
        mergeMap( action => {
            this.store.dispatch( SavedRepliesActions.DeleteLoading({ isLoading: true }) );
            return this.savedRepliesService.deleteSavedReply(action.id).pipe(
                tap(res => {
                    this.store.dispatch( SavedRepliesActions.SavedReplyDeleteSucess({ id: action.id }));
                    this.toastr.success( 'Saved Reply has been successfully deleted');
                }),
                catchError((error) => {
                    this.store.dispatch( SavedRepliesActions.SavedReplyDeleteFailed({message: error.message}) );
                    this.toastr.error( error.message, 'Something went wrong');
                    this.store.dispatch( SavedRepliesActions.DeleteLoading({ isLoading: false }) );
                    return empty();
                })
            );
        }),
        map(() => {
            return SavedRepliesActions.DeleteLoading({ isLoading: false });
        }),
    ));

Solution

You can opt for a more reactive way (using RxJS powerful), and so simplify a little your code with something like this:

deleteSavedReply$ = createEffect(() => this.actions$.pipe(
  ofType(SavedRepliesActions.SavedReplyDeleteRequested),
  mergeMap(action => this.savedRepliesService.deleteSavedReply(action.id).pipe(
    switchMap(res => [
      SavedRepliesActions.SavedReplyDeleteSucess({ id: res.id }),
      UiActions.showToastrSuccess('Saved Reply has been successfully deleted')
    ]),
    catchError(error => of(
      SavedRepliesActions.SavedReplyDeleteFailed({ message: error.message }),
      UiActions.showToastrError(error.message, 'Something went wrong')
    ]))
  ))
))

To do this, in the redux mindset, you should :

Create 2 new actions UiActions.showToastrSuccess and UiActions.showToastrError to show a message Toastr. Displaying a message is a could target for an action.
Use reducer to your loading flag. It's a slice of your state, so should change its value inside a reducer in place of the effect.

For example :

on(SavedRepliesActions.SavedReplyDeleteFailed, (state) => ({
  ...state,
  loading: false
})),

on(SavedRepliesActions.SavedReplyDeleteRequested, (state) => ({
  ...state,
  loading: true
})),

Other option

Note that another option (or improvment...) could be to dispatch Toastr actions, inside SavedReplyDeleteSucess action. For example :

deleteSavedReply$ = createEffect(() => this.actions$.pipe(
  ofType(SavedRepliesActions.SavedReplyDeleteRequested),
  mergeMap(action => this.savedRepliesService.deleteSavedReply(action.id).pipe(
    map(res => SavedRepliesActions.SavedReplyDeleteSucess({ id: res.id }))
    catchError(error => of(SavedRepliesActions.SavedReplyDeleteFailed({ message: error.message })))
  ))
))

savedReplyDeleteSucess$ = createEffect(() => this.actions$.pipe(
  ofType(SavedRepliesActions.SavedReplyDeleteSucess),
  map(_ => UiActions.showToastrSuccess('Saved Reply has been successfully deleted'))
))

savedReplyDeleteFailed$ = createEffect(() => this.actions$.pipe(
  ofType(SavedRepliesActions.SavedReplyDeleteFailed),
  map(message => UiActions.showToastrError(error.message, 'Something went wrong'))
))

The advantage here is that you can make your code evolving, by adding some extra effects in case of success or failure. for example:

savedReplyDeleteFailed$ = createEffect(() => this.actions$.pipe(
  ofType(SavedRepliesActions.SavedReplyDeleteFailed),
  switchMap(message => [
    UiActions.showToastrError(error.message, 'Something went wrong')),
    SystemActions.sendTraceError(error)
))

Hope it will help.