title: Disable button if input length less than 3
body: <p>I want to <strong>disable</strong> button if input <strong>length is less than 3</strong>:</p>
  
  <pre><code> &lt;input type="text" [(ngModel)]="newListItem"&gt;
   &lt;button [disabled]="{ disabled : newListItem.length &lt; 3 }"&gt;&lt;/button&gt;
  </code></pre>
  
  <p>But this code doesn't work. How can I achieve my goal?</p>