RxJS Observables nested subscriptions?

Previously answered for RxJS 5, I ended up on this page whilst using 6.

In the case you're on 6 as well (and I think you should be by now) you can use flatmap as an operator within pipe.

Modified the example code of @user3743222:

this.returnsObservable1(...)
  .pipe(
    flatMap(success => this.returnsObservable2(...)),
    flatMap(success => this.returnsObservable3(...))
  )
  .subscribe(success => {(...)}); 

The switchMap operator can also be useful. Some examples which describe the usefulness of switchMap compared to nested subscriptions can be found here:

1. situation with nested subscriptions

This codepen gives a demo: https://codepen.io/anon/pen/zdXBvP?editors=1111

Rx.Observable
  .interval(5000)
  .subscribe((val) => {
    console.log("outer:", val);
    Rx.Observable
      .interval(1000)
      .subscribe((ival) => {
        console.log("inner:", val, ival); 
      });
  });

2. situation with switchMap

This codepen gives a demo: https://codepen.io/anon/pen/xLeOZW?editors=1111

Rx.Observable
  .interval(5000)
  .switchMap((val) => {
    console.log("outer:", val);
    return Rx.Observable.interval(1000).map((ival) => [val, ival]);
  })
  .subscribe((val) => {
    console.log("inner:", val[0], val[1]);
  });

As mentioned in comments, you are looking for the flatMap operator.

You can find more details in previous answers :

• How to do the chain sequence in rxjs
• Why do we need to use flatMap?

Your example would read as :

this.returnsObservable1(...)
  .flatMap(success => this.returnsObservable2(...))
  .flatMap(success => this.returnsObservable3(...))
  .subscribe(success => {(...)});