angular 2 check if service is completed

Question

How can I check if a service is completed then run rest of the code?
example:
I want to get some data from API like this:

get_user_info(token: string): Observable<any> {
    return this.http.get(this.home + 'api/home/account/excerpt?token=' + token)
     .map((response: Response) => {
        return response.json().result;
     });
}

and I want to subscribe the data from get_user_info:

retrieve_user_info() {
    this.http.get_user_info(this.back_result.token).subscribe(
        (result: sendBackUserInfo) => {
            if (result.result == 1) {
                this.user_info = result.user;
            } else {
                console.log(result.messages[0]);
            }
        }
    );
}

but the problem is when I call the function retrieve_user_info, it doesn't get data immediately.
how can I fix that?

EDIT:
this is how I call retrieve_user_info:

submit_login_form() {
this.http.login_user(this.username, this.password, this.result.language.code)
    .subscribe((result: loginSendBackResult) => {
        this.back_result = result;
        this.retrieve_user_info();
        if (this.back_result.result == 1) {
            this.show_modal = false;
            console.log(user_info);
            router.navigate(['home']);
        }
    });
}

Answer 1

You can use flatMap to chain your requests. Also your naming made me a bit confused. When referring to service method, I would name the service something like service instead of http to separate where we are making a http-request and where we are calling a method in the service. So I used service here on those places instead.

import "rxjs/add/operator/mergeMap";

submit_login_form() {
  this.service.login_user(...)
    .flatMap((result: loginSendBackResult) => {
        this.back_result = result;
        return this.retrieve_user_info();
    });
    .subscribe(data => {
        if(this.back_result.result == 1) { 
           console.log(this.user_info)
           ....
        }
    })
}

and your retrieve_user_info()

retrieve_user_info() {
  return this.service.get_user_info(this.back_result.token)
     .map((result: sendBackUserInfo) => {
        if (result.result == 1) {
           return this.user_info = result.user;
        } else {
           console.log(result.messages[0]);
        }
     });
}