how to calculate date difference?

dear experts,

I have 2 form, A and B.

Form B contain the list of dates (7 dates) and the calculation executed here

Form B also act as subform in form A

below is the codes to calculate the difference between dates,

It works perfectly when in preview mode. but the scipt would not work when i place form B as subform

<script type="text/javascript">

$(function(){
$('input[name="dateStart"], input[name="dateEnd"]').change( function(){
      d1 = $('input[name="dateStart"]').datepicker('getDate');
      d2 = $('input[name="dateEnd"]').datepicker('getDate');
      diff = 0;
      
      diff = Math.floor((d2.getTime() - d1.getTime()) / 86400000); // ms per day
      diffy = Math.floor((d2.getTime() - d1.getTime()) / 86400000); // ms per day
      
      
      $('input[name=days1]').val(diff);
      $('input[name=datediff1]').val(diffy);
});

});