js 拖拽div

var rDrag = {

 o:null,

 init:function(o){

 o.onmousedown = this.start;

 },

 start:function(e){

 var o;

 e = rDrag.fixEvent(e);

 e.preventDefault && e.preventDefault();

 rDrag.o = o = this;

 o.x = e.clientX - rDrag.o.offsetLeft;

 o.y = e.clientY - rDrag.o.offsetTop;

 document.onmousemove = rDrag.move;

 document.onmouseup = rDrag.end;

 },

 move:function(e){

 e = rDrag.fixEvent(e);

 var oLeft,oTop;

 oLeft = e.clientX - rDrag.o.x;

 oTop = e.clientY - rDrag.o.y;

 rDrag.o.style.left = oLeft + 'px';

 rDrag.o.style.top = oTop + 'px';

 },

 end:function(e){

 e = rDrag.fixEvent(e);

 rDrag.o = document.onmousemove = document.onmouseup = null;

 },

 fixEvent: function(e){

 if (!e) {

 e = window.event;

 e.target = e.srcElement;

 e.layerX = e.offsetX;

 e.layerY = e.offsetY;

 }

 return e;

 } 

 };

 rDrag.init(obj);//obj is div object