;(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>