CODEWITHSUNDEEP
angularpromiserxjsobservable
Jonathan Eckman
Jonathan Eckman

Reputation: 2077

RxJS return empty promise but continue chain

I have a http service that I need to call depending on the users input. 

saveImage(): Observable<Photo> {
    if (!this.squaredImage) {
        return Observable.of();
    }

    this.photoCreateDto = {
        sourcePhoto: this.sourceImage,
        squaredPhoto: this.squaredImage,
        fileExtension: this.fileExtension
    };

    return this.photoService.createPhoto(this.photoCreateDto);
}

I call saveImage from another save function:

save() {
    this.saveImage().subscribe((newPhoto: Photo) => {

         .. never gets here

    });
}

If this.squaredImage has no value and the empty promise is returned, the chain ends. If the createPhoto service is called, it continues. I have also tried returning Observable.empty(). How do you handle this scenario in rxjs?

Upvotes: 3

Views: 1457

Answers (1)

martin
martin

Reputation: 96959

The problem is that you're handling only the next notifications with:

this.saveImage().subscribe((newPhoto: Photo) => { ... });

... while Observable.of() or Observable.empty() don't emit any next (they just send complete notifications).

So one thing you can do is to emit for example null and then in the subscriber check what value you sent:

saveImage(): Observable<Photo> {
    if (!this.squaredImage) {
        return Observable.of(null);
    }
    ...
}

...

this.saveImage().subscribe((newPhoto: Photo) => {
    if (newPhoto === null) {
        // ...
    }

    // ...
})

Or you can listen to both next and complete notifications (but be aware that when you return this.photoService.createPhoto a complete notification is probably sent as well):

this.saveImage().subscribe({
  next: (newPhoto: Photo) => {...}
  complete: () => { ... }
})

Upvotes: 5

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