moving down selected option is not visible

Question

when i move the first option to the bottom, at some point i cannot see the option in the select list, can anyone help ?

$(document).ready(function() {
  $('input[type="button"]').click(function() {
    var $op = $('#select2 option:selected'),
      $this = $(this);
    if ($op.length) {
      ($this.val() == 'Up') ?
      $op.first().prev().before($op):
        $op.last().next().after($op);
    }
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select multiple id="select2">
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
  <option value="12">12</option>
  <option value="23">23</option>
  <option value="34">34</option>
  <option value="11">11</option>
  <option value="25">25</option>
  <option value="83">83</option>
  <option value="81">81</option>
  <option value="82">82</option>
  <option value="73">73</option>
</select>
<input type="button" value="Up">
<input type="button" value="Down">

Answer 1

Here is a solution with scrolling:

$('input[type="button"]').click(function() {
  var $op = $('#select2 option:selected'),
    $this = $(this);
  if ($op.length) {
    ($this.val() == 'Up') ?
    $op.first().prev().before($op):
      $op.last().next().after($op);
  }

  var $s = $('#select2');
  $s.scrollTop($s.scrollTop() + ($op.offset().top - $s.offset().top));

});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select multiple id="select2">
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
  <option value="12">12</option>
  <option value="23">23</option>
  <option value="34">34</option>
  <option value="11">11</option>
  <option value="25">25</option>
  <option value="83">83</option>
  <option value="81">81</option>
  <option value="82">82</option>
  <option value="73">73</option>
</select>
<input type="button" value="Up">
<input type="button" value="Down">

Note that you can still finetune it, and only make scroll when its needed, and have it at bottom (instead of top) when you scroll down