title: Check if one of formControl is dirty or changed
body: <p>I wanna check if one of formControlName of my formGroup is changed value. Since I have many formControl I want to find a smart way to control if one of this is changed.</p>
  
  <pre><code>&lt;div&gt;
      &lt;label class="font-weight-bold"&gt;{{ 'questionario_codiceDomanda' | translate }}&lt;/label&gt;
  
      &lt;input formControlName="codDomanda" class="questionario-input-border form-control" type="text"
          (keyup)="changeCodDomanda($event)"&gt;
  &lt;/div&gt;
  &lt;!-- testo domanda --&gt;
  &lt;div class="col-xs-5 col-sm-5 col-md-5 col-lg-5 form-group"&gt;
      &lt;label class="font-weight-bold"&gt;{{ 'questionario_testo' | translate }}&lt;/label&gt;
  
      &lt;textarea formControlName="testo" class="questionario-input-border form-control" type="text" rows="2" cols="90"
          (keyup)="changeTesto($event)"&gt;&lt;/textarea&gt;
  &lt;/div&gt;
  &lt;!--help domanda--&gt;
  &lt;div class="col-xs-5 col-sm-5 col-md-5 col-lg-5 form-group"&gt;
      &lt;label class="font-weight-bold"&gt;{{ 'questionario_help' | translate }}&lt;/label&gt;
      &lt;textarea formControlName="help" class="questionario-input-border form-control" type="text" rows="2"
          cols="90"&gt;&lt;/textarea&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I tried with ngOnChanges but it doesn't work. What is the best way to check?</p>