title: Sequential http requests angular 4
body: <p>I am trying to do sequential http requests in angular 4. I have one http request which returns an Observable object as follows:</p>
  
  <pre><code>repos$: Observable&lt;Repo[]&gt;;
  this.repos$ = this.candidateService.getCandidateList(); // this method performs the http request
  
  getCandidateList(){
  this.http.get&lt;Repo[]&gt;('https://api.github.com/user/repos', {headers});
  }
  </code></pre>
  
  <p>Each of the returned Repo objects contains a field called subscribers_url, that I need to extract and perform a GET request on. Is there any way to do this? I have tried using mergeMap but it didn't seem to work. </p>
  
  <p>EDIT:</p>
  
  <pre><code>  interface Repo {
    name: string;
    url: string;
    full_name: string;
    subscribers_url: string;
  }
  </code></pre>