title: Angular custom validator not firing when input untouched?
body: <p>I have a reactive form as following:</p>
  <pre class="lang-js prettyprint-override"><code>this.form = this.formBuilder.group({
    name: ['', Validators.required],
    email: ['', this.customValidator()]
  });
  </code></pre>
  <p>I also have a &quot;submit&quot; button with a <code>[disabled]</code> condition:</p>
  <pre class="lang-html prettyprint-override"><code>&lt;button [disabled]=&quot;form.invalid&quot; (click)=&quot;create()&quot;&gt;Create&lt;/button&gt;
  </code></pre>
  <p>If <code>email</code> input is untouched and I modify <code>name</code> input, <strong><code>customValidator</code> is not fired</strong> and <code>Create</code> button enables despite the <code>customValidator()</code> would return an error.</p>
  <p>On the other hand, the <code>name</code> control has a <code>Validators.required</code> validation that is fired even if the input is untouched, which is the desired behaviour.</p>
  <blockquote>
  <p><a href="https://stackblitz.com/edit/angular-custom-validator-dzmdoz?file=src/app/app.component.ts" rel="nofollow noreferrer">Example on stackblitz</a>: I want the <code>email</code> input to be required
  (and the create button to be disabled) when <code>name</code> has value on it even if <code>email</code> is untouched.</p>
  </blockquote>