title: Angular 5 take action on variable change
body: <p>I'm trying to figure out the best way to do change detection.  I've got some HTML like so:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;tr *ngFor="let element of elements"&gt;
      &lt;td&gt;
          &lt;input type="checkbox" [(ngModel)]="element.checked"&gt;
      &lt;/td&gt;
      &lt;td&gt;
          &lt;select [(ngModel)]="element.tag" (change)="tagChanged(element)" [disabled]="!element.checked"&gt;
  </code></pre>
  
  <p>When I uncheck the input field I want to force the element.tag value to be a certain value.   Should I just do an <code>(change)</code> attribute on the <code>input</code> like I did with the <code>select</code> or is there a better way?  The fact that I've bound the <code>ngModel</code> makes me wonder if I'm doing things the best way.</p>