/*
* jDoubleSelect jQuery plugin
*
* Copyright (c) 2010 Giovanni Casassa (senamion.com - senamion.it)
*
* Dual licensed under the MIT (MIT-LICENSE.txt)
* and GPL (GPL-LICENSE.txt) licenses.
*
* http://www.senamion.com
*
*/

(function ($) {
    jQuery.fn.jDoubleSelect = function (o) {

        o = $.extend({
            text: ""
        }, o);

        return this.each(function () {
            var el = $(this);
            var p = el.parent();
            var name1 = (el.attr('id') || el.attr('name') || el.attr('class') || 'internalName') + '_jDS';
            var name2 = name1 + "_2";

            groupSel = "";
            $(this).children().each(function (i) {
                // Verify disabled or selected group
                if ($(this).attr("disabled"))
                    s = " disabled ";
                else if ($(this).find(":selected").attr("value") || $(this).attr('selected')) {
                    s = " selected ";
                }
                else s = "";

                if ($(this).attr("label"))
                    groupSel += "" + $(this).attr("label") + "";
                else
                    groupSel += "" + $(this).text() + "";
            });
            $(this).hide().after("" + groupSel + "");

            $("#" + name1).bind("change keyup",function () {
                $("#" + name2).add($("#" + name2).prev()).remove();
                var o = el.find("optgroup[label=\"" + $(this).val() + "\"]").html();
                if (o) {
                    el.next().after(" " + (el.attr("data-doubleSelect-innerLabel") || "") + " " + o + "");
                    $("#" + name2).trigger("change");
                    p.removeClass("jDoubleSelect-showing1").addClass("jDoubleSelect-showing2");
                } else {
                    el.attr("value", $(this).val());
                    p.removeClass("jDoubleSelect-showing2").addClass("jDoubleSelect-showing1");
                }
            });

            $("#" + name2).live("change keyup", function () {
                el.attr("value", $(this).val());
            }).trigger("change");

            $("#" + name1).trigger("change")
        });
    };
})(jQuery);

`Great – but when I add a second select to my form, doubleselect takes control of that too and I get two empty dropdown boxes`

I’ve fixed the code and solved that problem. You can find the complete modified script at http://codaset.com/plusglobal/browniephp/source/master/blob/webroot/js/jquery.jDoubleSelect.js

(in only added an if statement in line 39)

			$("#"+name2).live("change", function(){
				// THIS IS VERY VERY SLOW IN FIREFOX
				//el.val($(this).val());
				el.attr("value", $(this).val());
--->			el.trigger("change");
			}).trigger("change");

		$(this).children().each(function(i) {
				// Verify disabled or selected group
				if ($(this).attr("disabled"))
					s = " disabled ";
				else if ($(this).find(":selected").attr("value")) {
					s = " selected ";
					}
				else s = "";
				if($(this).attr("label")){//check if the child is option group
					groupSel += ""+$(this).attr("label")+"";
				} else {
					groupSel += ""+$(this).html()+"";
				}
			});
			$(this).hide().after(""+groupSel+" "+o.text+"");

			$("#"+name1).change(function(){
				// REMOVE OLD ELEMENT, ADD NEW SELECT, BIND CHANGE EVENT AND TRIGGER IT
				$("#"+name2).remove();

				if(el.find("optgroup[label="+$(this).val()+"]").length > 0){//if option group
					el.next().next().after(""+el.find("optgroup[label="+$(this).val()+"]").html()+"");
				} else {//else option
					el.attr("value", $(this).val());
				}

				//el.val($("#"+name2).val());
				$("#"+name2).trigger("change");
			});

With original version 0.3, on Demo2 you have performance issue when selecting 2nd select.

This seems like fixing the issue:
FIND:

el.val($(this).val());

REPLACE WITH:

el.attr("value", $(this).val());

FIND:

el.next().next().after(""+el.find("optgroup[label="+$(this).val()+"]").html()+"");

AFTER ADD:

$("#"+name2).trigger("change");

Please insure that using `attr(”value”, value)` gives the same result as `val(value)`.