Javascript獲取鼠標位置及拖動函數

function mouseX(event) {
    if(!event){
        return window.event.clientX + (document.documentElement.scrollLeft || document.body.scrollLeft);
    }else{
        return event.pageX;
    }
}
function mouseY(event) {
    if(!event){
        return window.event.clientY + (document.documentElement.scrollTop || document.body.scrollTop);
    }else{
        return event.pageY;
    }
}
function Drag(){}
Drag.prototype.baseX = 0;
Drag.prototype.baseY = 0;
Drag.prototype.lastX = 0;
Drag.prototype.lastY = 0;
Drag.prototype.nowX = 0;
Drag.prototype.nowY = 0;
Drag.prototype.obD = null;
Drag.prototype.obM = null;
Drag.prototype.build = function(_obD,_obM){
    if(_obM){
        Drag.prototype.obM = _obM;
    }else{
        Drag.prototype.obM = _obD;
    }
    Drag.prototype.obD = _obD;
    Drag.prototype.obM.onmousedown = function(event) {
        Drag.prototype.lastX = mouseX(event);
        Drag.prototype.lastY = mouseY(event);
        Drag.prototype.baseX = Drag.prototype.obD.style.left;
        Drag.prototype.baseY = Drag.prototype.obD.style.top;
        this.onmousemove = function(event){
                Drag.prototype.nowX = mouseX(event);
                Drag.prototype.nowY = mouseY(event);
                Drag.prototype.obD.style.left = (parseFloat(Drag.prototype.baseX) + Drag.prototype.nowX - Drag.prototype.lastX) + "px";
                Drag.prototype.obD.style.top = (parseFloat(Drag.prototype.baseY) + Drag.prototype.nowY - Drag.prototype.lastY) + "px";
        }
    }
    Drag.prototype.obM.onmouseup = function(event){
        //obD.onmouseup = null;
        Drag.prototype.obD.onmousemove = null;
    }
    Drag.prototype.obM.onmouseout = function(){
        //obM.onmouseup = null
        Drag.prototype.obM.onmousemove = null;
    }
}

//使用方法
var drag = new Drag();

drag.build(getElementById("div"));//拖動本身
或
drag.build(getElementById("div"),getElementById("div"));//通過一個對象拖動另一個對象