jQuery Plugin num().html

<script type="text/javascript">
  jQuery(function($){
    $.fn.num = function(){
      var val = $(this).val();
      return (isNaN(val) || val == null) ? 0 : parseInt(val);
    }
  });
</script>

<!-- usage -->

<form id="sample">
	<input type="text" id="field" />
</form>

<script type="text/javascript">
  $('#sample').submit(function(){
    alert($('#field').num() * 10);
    return false;
  });
</script>