title: extends HTTP and call local method (error Symbol(Symbol.iterator)')
body: <h1>Update:</h1>
  
  <p>Hi what I'm trying: <code>extends Http</code> service and intercept error status of all my POST request, but I don't understant Why I can't access to my method getTicket() inside my interceptor ? </p>
  
  <p>My HttpService service file:</p>
  
  <pre><code>@Injectable()
  export class HttpService extends Http {
      public SERVER_URL: string = 'http://10.0.0.183:8080/alfresco/s/'
      public TICKET: string = ''
  
      constructor(backend: ConnectionBackend, defaultOptions: RequestOptions) {
          super(backend, defaultOptions);
      }
  
      post(url: string, body: any, options?: RequestOptionsArgs): Observable&lt;Response&gt; {
          console.log("ok POST")
          return this.intercept(super.post(url, body));
      }
  
      intercept(observable: Observable&lt;Response&gt;): Observable&lt;Response&gt; {
          return observable.catch((err) =&gt; {
  
              if (err.status == 401) {
                  this.getTicket().map(res =&gt; {
                      this.TICKET = res.json().data.ticket
                      return Observable.empty()
                  })
              } else {
                  return Observable.throw(err)
              }
  
          });
      }
  
      getTicket() {
          return this.post(this.SERVER_URL + 'api/login', JSON.stringify({
              username: 'admin',
              password: 'admin'
          }))
      }
  
      deleteDocument(idFile: number) {
          return this.post(this.SERVER_URL + 'dms/file/delfile?idfile=' + idFile + '&amp;alf_ticket=' + "jhgjkgjhg", {}).map((data: Response) =&gt; data.json())
  }
  }
  </code></pre>
  
  <p>in my app.module.ts</p>
  
  <pre><code> providers: [CommunicationInsideServices, TicketValidGuard, UserValidGuard, [
          {
              provide: HttpService,
              useFactory: (backend: XHRBackend, options: RequestOptions ) =&gt; {
                  return new HttpService(backend, options);
              },
              deps: [XHRBackend, RequestOptions ]
          }
      ]],
  </code></pre>
  
  <p>Is there a good soul :) to explain me how I can use my local method getTicket() inside interceptor ?!?! cause I get this error:
   Cannot read property 'Symbol(Symbol.iterator)' of undefined</p>
  
  <p>Thanks</p>