title: How to intercept the value of FormControl before setting or getting it?
body: <p>The question is pretty self-explanatory. I would like to intercept the incoming value for a FormControl's value property, and be able to intercept the outgoing value to the HTML control that it's hooked up to. </p>
  
  <p>Let's say I have a FormControl named "firstName" and I hook it up to a textbox as such:</p>
  
  <pre><code>&lt;input type="text" formControlName="firstName" /&gt;
  </code></pre>
  
  <p>By default, when the user inputs the value in the textbox and submits, the FormControl's value gets set to the value in the textbox. Is there any way I can intercept the value that gets set and modify it before setting it? </p>
  
  <p>Similarly, is there any way to intercept the value that the FormControl sends to the HTML control? For example if I have a FormControl's value set to something but I want to modify the value that shows up in the textbox. </p>
  
  <p>I know I can use ngModel to act as a mediator between the form and the control, but that gets cumbersome when using more than a few controls. I also know you can create your own control and implement the ControlValueAccessor, but this is also cumbersome as I would have to create a corresponding control for each control I want to use.</p>
  
  <p>For more information about why I'm asking this question, see <a href="https://github.com/ionic-team/ionic/issues/7121" rel="noreferrer">https://github.com/ionic-team/ionic/issues/7121</a></p>