ต้องการทำฟังก์ชั่น Jquery datepicker OnClose เมื่อเลือก วันที่แล้ว ให้คำนวณวันแสดงในอีก textbox นึง

<script>
 $(function() {
    $.datepicker.setDefaults( $.datepicker.regional[ "ko" ] );
    $( "#datepicker" ).datepicker({
    		showOn : "both",
    		defaultDate: "+1w",
            showOn: "button",
            numberOfMonths: 2,
            dateFormat: "yy-mm-dd",
            changeMonth: true,
            changeYear: true,
            showButtonPanel: true,
            buttonImage: "../images/btn_date.gif",
            buttonText: "Choose",
            onClose: function(selectedDate){
                $("#datepicker2").datepicker( "option", "minDate", selectedDate);
                dateOnClose($(this).attr("id"), selectedDate);
            }
    });

    $('#datepicker2').datepicker({
    		showOn : "both",
    		defaultDate: "+1w",
            showOn: "button",
            numberOfMonths: 2,
            dateFormat: "yy-mm-dd",
            changeMonth: true,
            changeYear: true,
            showButtonPanel: true,
            buttonImage: "../images/btn_date.gif",
            buttonText: "Choose",
			onClose:function(selectedDate){
				$("#datepicker").datepicker( "option", "maxDate", selectedDate );
				dateOnClose($(this).attr("id"), selectedDate);
			}
	});
 });


//Datepick Close Event
function dateOnClose(obj, date){
	if (date != "") {
		if (obj == "datepicker2") { 
			if ($('#datepicker').val() != ""){
				var diff = datediff("d", $('#datepicker').val(), $('#datepicker2').val());
				$("#day_rent").val(diff);
			}
		} else {
			$('#datepicker2').val($.datepicker.formatDate($.datepick.add(new Date(date), parseInt($("#day_rent").val()), "d") ));
		}
		
		if ($('#datepicker').val() > $('#datepicker2').val()){
				dayChoiceChange('datepicker', 'datepicker2', this.value, 0);
			$("#day_rent").val("1");
		}
	}
}