Is it good way to call subscribe inside subscribe?

Question

I need to pass three data to one function from three different APIs:

this.service.service1().subscribe( res1 => {   this.service.service1().subscribe( res2 => {     this.service.service1().subscribe( res3 => {       this.funcA(res1, res2, res3);   });   }); }); 

Is it a good practice to subscribe inside a subscribe?

Answer 1

The correct way is to compose the various observables in some manner then subscribe to the overall flow — how you compose them will depend on your exact requirements.

If you can do them all in parallel:

forkJoin(   this.service.service1(), this.service.service2(), this.service.service3() ).subscribe((res) => {   this.funcA(res[0], res[1], res[2]); }); 

If each depends on the result of the previous, you can use mergeMap (formerly known as flatMap) or switchMap:

this.service.service1().pipe(   mergeMap((res1) => this.service.service2(res1)),   mergeMap((res2) => this.service.service3(res2)) ).subscribe((res3) => {   // Do something with res3. }); 

... and so on. There are many operators to compose observables to cover lots of different scenarios.