原生javascript实现DIV拖拽并计算重复面积(3)

var Drag = {
    elem    : null,
    zindex  : 0,
    options : {},
    init    : function(){       
  each(arguments,function(i,elem,oThis){
    addListener(elem,'mousedown',BindAsEventListener(oThis,oThis.start,elem));
  },this);
    },
    start : function(e,elem){
        var elem=this.elem = elem;
        elem.style.zIndex=++this.zindex;
        this.x = e.clientX - elem.offsetLeft ;
        this.y = e.clientY - elem.offsetTop;
        this.marginLeft = parseInt(currentStyle(elem).marginLeft)||0;
        this.marginTop  = parseInt(currentStyle(elem).marginTop)||0;
        Sys.ie?elem.setCapture():e.preventDefault();
        addListener(document,"mousemove",BindAsEventListener(this,this.move));
        addListener(document,"mouseup",Bind(this,this.up)); 
  this.options.callbackmove&&this.options.callbackmove(this.elem);
    },
    move  : function(e){
        window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty();
        var iLeft = e.clientX - this.x,iTop = e.clientY - this.y;obj = this.elem;
        obj.style.left = iLeft - this.marginLeft + "px";
        obj.style.top  = iTop - this.marginTop + "px";
        this.options.callbackmove&&this.options.callbackmove(this.elem);
    },
    up   : function(){
        removeListener(document,'mousemove');
        removeListener(document,'mouseup');
        Sys.ie&&this.elem.releaseCapture();
        this.options.callbackup&&this.options.callbackup(this.elem);
    }
};