rxjs - how to make 2 dependent http request in Angular 2

Question

i need to make 2 http request (the second dependent on the first) to insert user credentiels into my data base.

the first service get the user credentiels (http://localhost:55978/FleetViewDBWebService.asmx/ChekCreds?name=name1&subname=subname1) and check if the user already exist or not, return the 'ID' if it exist , or "ok" if the user doesn't exist.

then i need to subscribe to the first service and get the returned value. if "ok" call the second service (http://localhost:55978/FleetViewDBWebService.asmx/InsertUser?name=name1&subname=subname1&Telephone=334580021)
to insert the user credentiels , else return any message .

I call the first service and get the result but i have no idea how to add the second service.

is there any ideas

service.ts

CheckCreds(value: any) {
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });

    let params = new URLSearchParams();



    params.set('name', (value.nom).toString());
    params.set('subname', (value.prenom).toString());

    return this.http.get(this.checkUri, {
        search: params, withCredentials: true
    })
        .map(res => {
            console.log("++++" + res.text());


            return JSON.parse(res.text());
        })
        .catch(this.handleError)


} 

component.ts

 submitForm($ev, value: any) {
    $ev.preventDefault();
    for (let c in this.valForm.controls) {
        this.valForm.controls[c].markAsTouched();
    }
    if (this.valForm.valid) {
        this.Service.CheckCreds(value)
            .subscribe(
            res => {
                string result=JSON.stringify(res);
            },
            e => {
                alert(e);
            },
            () => {
            }

            );

    }
}

Answer 1

The RxJS way would be to use the switchMap operator to wait for the response of the first request to arrive before firing the second request.

return this.http.get('url/1')
  .switchMap(res1 => {
    // use res1 to further control param of the second call
    this.http.get('url/2')
  })
  .subscribe(res2 => {
    //do stuff with the second response
  })

---

To do the requests in parallel (for requests which are not dependant of one another), use the forkJoin static operator.

return Observable.forkJoin(
  this.http.get('url/1'),
  this.http.get('url/2'),
)
  .subscribe(([res1, res2]) => {
    // res1 and res2 available after both requests are completed
  })