javascript dragable的Move对象

var Move = {
$: function(id){
return (typeof id == "object") ? id : document.getElementById(id);
},
pageX: function(elem){ //获取目标elem的X坐标
return elem.offsetParent ? //如果能继续得到上一个元素，增加当前的偏移量并继续向上递归
elem.offsetLeft + this.pageX(elem.offsetParent) : elem.offsetLeft;
},
pageY: function(elem){ //获取目标elem的Y坐标
return elem.offsetParent ? elem.offsetTop + this.pageX(elem.offsetParent) : elem.offsetTop;
},
make: function(id){
var elem = this.$(id);
var oldXY = null;
var newXY = null;
var x = 0; //记录初始化是目标elem的x坐标
var y = 0; //记录初始化是目标elem的y坐标
var t = this;
elem.onmouseover = function(e){
this.style.cursor = "default";
}
elem.onmousedown = function(e){
e = e || window.event;
this.style.position = "absolute";
this.style.cursor = "move";
x = t.pageX(this);
y = t.pageY(this);
var that = this;
oldXY = {
x: e.clientX,
y: e.clientY
}; //获取鼠标在按下的时候的坐标
document.onmousemove = function(e){
e = e || window.event;
newXY = {
x: e.clientX,
y: e.clientY
}; //获取鼠标在移动过程中的坐标
that.style.left = (newXY.x - oldXY.x + x) + "px";
that.style.top = (newXY.y - oldXY.y + y) + "px";
that.style.zIndex = "100";
}
}
elem.onmouseup = function(e){
this.style.cursor = "default";
this.style.zIndex = "0";
document.onmousemove = function(e){ //在放开鼠标的时候覆盖掉mousemove事件函数
return;
}
}
}
}