title: property length does not exist on type Object
body: <p>I have a services that get's a JSON from docker. I want to get the amount of containers.</p>
  
  <p>So I subscribe to my service: </p>
  
  <pre><code>ngOnInit() {
      this.docker.getContainers().subscribe(containers =&gt; {
          console.log(containers.length);
      });
  }
  </code></pre>
  
  <p>I get the right answer on the console and yet I get: </p>
  
  <blockquote>
    <p>property length does not exist on type Object</p>
  </blockquote>
  
  <p>Am I doing something wrong?</p>
  
  <pre><code>export class DockerService {
    private baseUrl:string = 'http://localhost:8080/api/docker';
    private headers = new HttpHeaders({'Content-Type':'application/json'});
    private options = new HttpHeaderResponse({headers:this.headers});
  
    constructor(private _http:HttpClient) { }
  
    getContainers() {
      return this._http.get(this.baseUrl + "/containers", this.options);
    }
  
    getImages() {
      return this._http.get(this.baseUrl + "/images", this.options);
    }
  }
  </code></pre>