JQuery Draggable Demo

// Simple jQuery Draggable Plugin
// https://plus.google.com/108949996304093815163/about
// Usage: $(selector).drags();
// Options:
// handle            => your dragging handle.
//                      If not defined, then the whole body of the
//                      selected element will be draggable
// cursor            => define your draggable element cursor type
// draggableClass    => define the draggable class
// activeHandleClass => define the active handle class
//
// Update: 26 February 2013
// 1. Move the `z-index` manipulation from the plugin to CSS declaration
// 2. Fix the laggy effect, because at the first time I made this plugin,
//    I just use the `draggable` class that's added to the element
//    when the element is clicked to select the current draggable element. (Sorry about my bad English!)
// 3. Move the `draggable` and `active-handle` class as a part of the plugin option
// Next update?? NEVER!!! Should create a similar plugin that is not called `simple`!

(function($) {
    $.fn.drags = function(opt) {

        opt = $.extend({
            handle: "",
            cursor: "move",
            draggableClass: "draggable",
            activeHandleClass: "active-handle"
        }, opt);

        var $selected = null;
        var $elements = (opt.handle === "") ? this : this.find(opt.handle);

        $elements.css('cursor', opt.cursor).on("mousedown", function(e) {
            if(opt.handle === "") {
                $selected = $(this);
                $selected.addClass(opt.draggableClass);
            } else {
                $selected = $(this).parent();
                $selected.addClass(opt.draggableClass).find(opt.handle).addClass(opt.activeHandleClass);
            }
            var drg_h = $selected.outerHeight(),
                drg_w = $selected.outerWidth(),
                pos_y = $selected.offset().top + drg_h - e.pageY,
                pos_x = $selected.offset().left + drg_w - e.pageX;
            $(document).on("mousemove", function(e) {
                $selected.offset({
                    top: e.pageY + pos_y - drg_h,
                    left: e.pageX + pos_x - drg_w
                });
            }).on("mouseup", function() {
                $(this).off("mousemove"); // Unbind events from document
                if ($selected !== null) {
                    $selected.removeClass(opt.draggableClass);
                    $selected = null;
                }
            });
            e.preventDefault(); // disable selection
        }).on("mouseup", function() {
            if(opt.handle === "") {
                $selected.removeClass(opt.draggableClass);
            } else {
                $selected.removeClass(opt.draggableClass)
                    .find(opt.handle).removeClass(opt.activeHandleClass);
            }
            $selected = null;
        });

        return this;

    };
})(jQuery);