title: How replace status for another with ngClass
body: <p>I like to have two state in on NgClass.
  When the status is true and class success it display text 'On'
  When it's false and class warning it display text 'Off'
  but if the status error is true , class danger I just need to display only 'Problem'</p>
  
  <pre><code>&lt;td mat-cell class="status" *matCellDef="let element" [ngClass]="{
                        'alert alert-success': element.status ,
                        'alert alert-warning': element.status === false
                        ,'alert alert-danger' : element.error}"
                        &gt; {{element.status ? 'On' : 'Off'}} &lt;/td&gt;
  </code></pre>