How to chain rxjs observable

I am coming from Angular1, and like chaining promise, I want to have similar behavior.

I have a method in someclass:-

{.........
      doLogin (username, password) {
            .......
            .......
            return this.http.get(api).subscribe(
                    data => {.....}, //enters here
                    err => {.....}
        }

Then I am calling this method :-

 someclass.doLogin(username, password).subscribe(
           data => { }, //Not getting called
            err => { }
 }

As I mentioned as comments on the above code, the subscribe is not getting called in the caller class.

Any suggestion about how to do this ?

---

In fact, you return the object of the subscribe method. It's a subscription and not an observable. So you won't be able to subscribe (again) to the returned object.

Observables allows to build data flow chain based on observable operators. It depends on what you want to do.

If you simply trigger something or set a service property from your service, you could use the do operator and the catch one for error handling:

doLogin (username, password) {
  .......
  .......
  return this.http.get(api).do(data => {
    .....
    // Call something imperatively
  })
  .catch(err => {
    .....
    // Eventually if you want to throw the original error
    // return Observable.throw(err);
  });
}

Don't forget to include these operators since they aren't included out of the box by Rxjs:

import 'rxjs/add/operator/do';
import 'rxjs/add/operator/catch';

or globally (all operators):

import 'rxjs/Rx';

See related questions:

Angular 2, best practice to load data from a server one time and share results to components

Angular 2 HTTP GET with TypeScript error http.get(...).map is not a function in [null]

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