title: In Angular, how to add Validator to FormControl after control is created?
body: <p>We have a component that has a dynamically built form. The code to add a control with validators might look like this:</p>
  <pre class="lang-js prettyprint-override"><code>var c = new FormControl('', Validators.required);
  </code></pre>
  <p>But let's say that I want to add 2nd Validator <strong>later</strong>. How can we accomplish this? We cannot find any documentation on this online. I did find though in the form controls there is <code>setValidators</code></p>
  <pre class="lang-js prettyprint-override"><code>this.form.controls[&quot;firstName&quot;].setValidators 
  </code></pre>
  <p>but it is not clear how to add a new or custom validator.</p>