title: Angular 2 FormGroup Add Validators dynamic
body: <p>i'm tring to add validator to FormContol dynamic (not on initialization) and it's not work....</p>
  
  <p>the code: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>this.formGroup.controls["firstName"].validator = Validators.Required;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Did anyone do it? </p>