;(function($){

    $.fn.extend({

            "jLzindex" : function(){    //用于判断和设置各个对话框的z-index

                var $dragIndex = $(this);

                var arrzIndex = new Array();

                for(var i=0; i < $dragIndex.length; i++){    //初始化数组元素值，并按拖拽项顺序设置z-index值

                    var zIdxNum = 10000 - i - i -2;

                    arrzIndex[i] = {"getId":"drag" + ($dragIndex.length - i),"zIdx":zIdxNum};

                    $("#drag" + ($dragIndex.length - i)).css("z-index",zIdxNum);

                }

               $dragIndex.mousedown(function(){

                    var i = 0;

                    var dIndex = 0;

                    while(arrzIndex[i]){    //找到当前点击项在数组里的下标

                        if(arrzIndex[i].getId == $(this).attr("id")){ dIndex = i;}

                        i++;

                    }

                    for(var i = dIndex; i >=0; i--){    //把点击项移至数组第一位，其他项后移

                        if(i > 0){

                            arrzIndex[i].getId = arrzIndex[i-1].getId;

                            $("#" + arrzIndex[i].getId).css("z-index",arrzIndex[i].zIdx);

                        } else{

                            arrzIndex[i].getId = $(this).attr("id");

                            $("#" + arrzIndex[i].getId).css("z-index",arrzIndex[i].zIdx);

                        }

                    }

                });

            },

            "jLdraggable" : function(mod){    //拖拽插件

                var model = mod;

                var draggable = false;

                var $drag = $(this);

                $drag.find(".dragBar").mousedown(function(e){

                    draggable = true;

                    var mouseLeft = e.pageX - $drag.find(".dragBar").offset().left;    //鼠标在拖拽区域中的横向距离

                    var mouseTop = e.pageY - $drag.find(".dragBar").offset().top;    //鼠标在拖拽区域中的横向距离

                    if(model == "cFade"){    //原位置元素半透明

                        $drag.clone(false).appendTo("body").addClass("dragShadow").fadeTo(0,0.2).css("z-index",parseInt($drag.css("z-index")) - 1);

                    } else if(model == "dFade"){    //跟随鼠标元素半透明

                        $drag.clone(false).appendTo("body").addClass("dragShadow").css("z-index",parseInt($drag.css("z-index")) - 1);

                        $drag.fadeTo(0,0.2);

                    }

                    $(document).mousemove(function(e){

                        if(draggable){

                            var winWidth = $(window).width();

                            var winHeight = $(window).height();

                            var dragLeft = e.pageX - mouseLeft;

                            var dragTop = e.pageY - mouseTop;

                            //拖拽框不能超出窗口边界

                            if(dragLeft < 0){dragLeft = 0;}

                            if(dragLeft + $drag.width() > winWidth){

                                dragLeft = winWidth - $drag.width();

                            }

                            if(dragTop < 0){dragTop = 0;}

                            if(dragTop + $drag.height() > winHeight){

                                dragTop = winHeight - $drag.height();

                            }

                            $drag.css("left",dragLeft + "px");

                            $drag.css("top",dragTop + "px");

                        } else{

                            return false;

                        }

                    });

                });

                $(document).mouseup(function(){

                    draggable = false;

                    $(".dragShadow").remove();

                    if(model == "dFade"){

                        $drag.fadeTo(0,1);

                    }

                });

            }

        })

})(jQuery)

<script type="text/javascript" src="js/jquery.min.js"></script>

<script type="text/javascript" src="js/jquery.jLdraggable.js"></script>

<script type="text/javascript">

$(document).ready(function(){

    $("#drag1").jLdraggable(); //无参数，没有影子

    $("#drag2").jLdraggable("cFade");  //cFade，定义原位置半透明阴影

    $("#drag3").jLdraggable("dFade");  //dFade，定义跟随鼠标的半透明阴影

    $(".dragIndex").jLzindex();  //多个窗口的z-index处理

});

</script>

<style type="text/css">

.dragTitle{

    width:120px;

    height:27px;

    background:url(images/drag_01.jpg);

    cursor:move;

}

.dragContent{

    width:120px;

    height:73px;

    background:url(images/drag_02.jpg);

    line-height:73px;

    text-align:center;

}

#drag1{

    width:120px;

    position:absolute;

    left:10px;

    top:10px;

}

#drag2{

    width:120px;

    position:absolute;

    left:90px;

    top:90px;

}

#drag3{

    width:120px;

    position:absolute;

    left:170px;

    top:170px;

}

</style>

<div id="drag1" class="dragIndex">

  <div class="dragBar dragTitle"></div>

  <div class="dragContent">无参数</div>

</div>

<div id="drag2" class="dragIndex">

  <div class="dragBar dragTitle"></div>

  <div class="dragContent">原位半透明</div>

</div>

<div id="drag3" class="dragIndex">

  <div class="dragBar dragTitle"></div>

  <div class="dragContent">拖拽半透明</div>

</div>