angular is promise. You can string the operation with the asynchronous request

use callback, the following pseudo code

//

//
.success((//))

if it is cyclic asynchronous, you can use recursion

//

 A(){
    //
    .success((A()))
}

you can first encapsulate a layer of http requests, such as post (url, data = {}, headers = this.headers ()) {

url = this.handle(url);
return this.http.post(url, data, { headers: headers })
  .map(response => response.json())
  .catch(error => this.errorNotice(error));

}
then write the service or directly introduce postSomething (params: any): Observable {

const url = Constant.serverIp + Constant.api.someApi;
return this.DHttp.post(url, params).map(res => res);

}
Last subscription
this.postSomething (this.params) .subscribe (res= > {}, err= > {})

first of all, the http.get () / post () return type in angular is Observable < response > , not promise .

but Observable can be converted to promise, so this is to use async await to make the code look Synchronize.

  obsevable: Observable<Response> = this.http.get("url", {headers: headers});
  async testObservable() {
    //
    .....
    //
    let response: Response = await this.obsevable.toPromise();
    //
    .....
  }