title: how to disable/enable dropdown angular 4
body: <p>How can I enable/disable a dropdown based on the selection of another dropdown menu?</p>
  
  <p>I tried this but it doesn't seem to work:</p>
  
  <pre><code>&lt;select class="custom-select" id="abc"&gt;
      &lt;option value="" hidden&gt;Select&lt;/option&gt;
      &lt;option *ngFor="let data of datay" 
              [ngValue]="data.code" 
              [attr.disabled]="true"&gt; 
          {{data.name}}
      &lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>Any sample code is appreciated.</p>