Change a « Choice with Fill-In » field into a magic dropdown [Sharepoint]

Sometimes you want to modify the options for a dropdown box by removing some existing options, however you want to be able to keep these old values for reporting or whatever reasons.

Below is a way to do it by using jQuery and SharepointPlus. It will hide the « Specify your own value » stuff, and add the old value (if any) into the dropdown selection.

For example if you have a Choice field with options « A », « B », « C ». Your item ID #1 has value « B ».
After a while you decide to delete « B » and add « D », but you want to be able to find items with the « B » value.
So you choose « Choice with Fill-In » and apply the below code:

// For flexibility reasons we create them as a Choice with Fill-In option,
//    however we hide the free text field and we show only the dropdown
//    in case of the fill-in has a value, then we add it into the list of options
$SP().formfields(["My Fist Dropdown", "Another One"]).each(function() {
  var $e = this.elem();
  // hide all except the dropdown
  //$e.not('select').hide().filter(':radio:last').closest('tr').hide(); // SP2010
  $e.eq(0).closest('table').find('tr:gt(0)').hide(); // SP2013
  // if we have a value into the fill-in box, then:
  //   - add it into the options
  //   - when another value is selected we check the first checkbox
  var fillValue = $e.last().val();
  if (fillValue) {
    $e.filter('select').append('<option data-fillin="true">'+fillValue+'</option>').each(function() {
      var $this=$(this);
      $this.find('option:last').prop("selected", true);
      $this.removeAttr("onclick").on('change', function(event) {
        var $opt = $(this).find(':selected');
        if ($opt.data("fillin")) {
          $e.filter(':radio:last').prop("checked", true);
        } else {
          $e.filter(':radio:first').prop("checked", true);
        }
      });
    });
  }
})

So now, if you create a new item you’ll see a dropdown with « A », « C », and « D » only.
But if you edit your item #1, you’ll have a dropdown with « A », « C », « D » and « B ».