title: Use updateOn: 'blur' in Angular Reactive Forms
body: <p>I would like to start the validation of the fields of my forms only when the user leave the field (<code>onblur</code>).</p>
  
  <p>I'm trying in this way:</p>
  
  <pre class="lang-js prettyprint-override"><code>    this.profileForm = this.fb.group({
                  firstName: ['initial value',
                      [Validators.required, Validators.minLength(2), forbiddenNameValidator(/bob/i)],
                      [forbiddenNameValidatorAsync()],
                      { updateOn: 'blur' }
                  ],
                  lastName: ['b']
              });
  
  </code></pre>
  
  <p>But in this way it does not work.
  The validations (sync and async) are performed during onChange.</p>
  
  <p>I would also like to ask how you can verify the name by making checks on the <code>lastName</code>.</p>
  
  <p>Example: I would like the name field to be disabled if it is the same as the last name (only name field, not entire form not both fields).</p>