[jQuery] about dragging and get new parent()

Hi
I am trying to do something but I did not do this. I am using
draggable function. When I stop my dragged element, I want to learn
new parent element, if it is true, drop element but if it is not,
reverse droping and turn back.
<script type="text/javascript">
$(document).ready(function(){
    $('#mydiv').draggable({ stop: function(event, ui) {
        var parent = document.getElementById('mydiv').parentNode.id;
alert(parent);
     } });
});
</script>