why is my jquery change() method not getting executed in jira?

Question

hello,

more jira issues. I've got a customfield that i've atatched a change() method to. The plan is to update the built in version field when my custom field changes but at the moment the code never gets executed.

<script type="text/javascript">
 jQuery(function($){
   $('#customfield_10004').change(function(){
      alert("changing");
      $('#versions').val($('#customfield_10004 option:selected').val());
      alert($('#customfield_10004 option:selected').val());
   });
 });
</script>

I never get to the popup window.

The customfield_10004 is a single version picker and the versions is the built in affected Version/s field. The reason i'm doing this is i dont want a user to select more than one version but i dont know where or how to put some conditions on the built in field.

Lots of plugins rely on this built in field so i need it to be set somehow.