title: How to add zeros into HTML input?
body: <p>I have a html input that has a fixed length of 7.
  If the users types 1234, how can I prefix this input with a number of zeros in order to have the required length of 7?</p>
  
  <p>I want to do this only in the UI because I already have a method in ts code for prefixing with zeros this input in order to send this correctly to backend.</p>
  
  <pre><code> &lt;input formControlName="userNumber" type="text" class="form-control" placeholder="User #" aria-label="userNumber" aria-describedby="userNumber"&gt;
  </code></pre>