title: Add a permanent prefix to a textbox
body: <p>What I am trying to achieve is to force a textbox to start with a prefix ( country telephone code ) and to make this permanent, meaning that the user cannot bypass this. For example, the Phone textbox should always start with "+45" and after that the user can add the phone number. How to prevent it from deleting the code, by any means?</p>
  
  <p>What I done so far, using jQuery:</p>
  
  <pre><code>//attach event on phone text boxes
  $(document).delegate(".phone", "keyup", function(event){
  
  var target = $(this);
  
  var value = target.val().trim();
  
  if (value.indexOf(CONSTANTS.DANISH_PHONE_CODE) == -1) {
      //country code not found
  
      //if the user starts deleting the country code 
      if (value.indexOf("+") == 0){
          value = "";
      }
  
      //if the user types something in front of the country code, put the country code at the end
      value = value.replace(CONSTANTS.DANISH_PHONE_CODE, "");
  
      //phone doesn't start with +45
      value = CONSTANTS.DANISH_PHONE_CODE + value;
  
      target.val(value); 
  }
  
  
  });
  </code></pre>
  
  <p>But the problem is that the user can delete the plus sign and the prefix is put automatically at the start so we will have +4545. Do you know an elegant way of achieving this? Thanks.</p>