gistfile1.txt

  <div class="field" id="head_count">
    <label for="hard_drive_head_count">Head count</label><br />
    <input id="hard_drive_head_count" name="hard_drive[head_count]" type="number" value="0" />
    <script type="text/javascript">
document.getElementById("head_count").innerHTML=$(this.children[this.selectedIndex])+ " jjj";
      $("#head_count").change(function() {
        var selopt = $(this.children[this.selectedIndex]),
        isCredit = parseInt(selopt.attr('data-iscredit'));
        if (isCredit === 0) {
          $("#head_count").hide();
        } else {
          $("#head_count").show();
        }
      })
    </script>
  </div>