```
this.pokojeService.pobierzPokoje().subscribe(pokoje => {
  this.pokoje = pokoje;
});
this.pokojeService.pobierzTypyPokoi().subscribe(pokojeTypy => {
  this.pokojeTypy = pokojeTypy;
});

```

those are my 2 observables. 
I want to iterate on pokoje and pokojetypy, but what if one of them return error, not data?
I want to prevent that and check if both of them returned data successfully