title: Angular 2 Reactive Forms: update select list on value changes
body: <p>I have an Angular 2 form built using ReactiveForms. The form contains 2 select elements. The first one contains a list of vehicle makes. When a make is selected from the list, the second select element should show the models belonging to that make. </p>
  
  <p>I've been playing around with valueChanges, but I can't seem to get the second(child) select element to contain the models for the selected make. When both fields are just simple input elements, reacting on valueChanges does in fact update the model input element (using the setValue on the model FormControl). See below code sample for simple input fields.</p>
  
  <p>Is it even possible to accomplish this with Reactive Forms?</p>
  
  <pre><code>this.vehicleForm.controls['make'].valueChanges.subscribe((value) =&gt; {
    console.log(value);
    this.vehicleForm.controls['model'].setValue('Some Value');
  });
  </code></pre>
  
  <p>In this case the 'value' is in fact the selected make object. </p>