工作需要写的一个js拖拽组件

/* 
*使用方法： 
* var d = new Drag({id:'dragPannel',maxLeft:500,maxTop:200}); 
* d.ready(); 
*请注意： 
* 拖动对象的left和top样式必须写在其style属性里边 
* 
*/ 
//矫正调用者。将 fn 作为 newObj 的方法调用 
function repairCaller(newObj, fn){ 
return function(){ 
return fn.apply(newObj, arguments); 
} 
} 
function Drag( config ){ 
this.moveTarget = T.dom.get( config.id ); 
this.startLeft = parseInt(this.moveTarget.style.left); //每次拖动开始时被拖动对象的 left,top 
this.startTop = parseInt(this.moveTarget.style.top); 
this.startClientX = this.startLeft; //保存拖动开始时事件的 clientX, clientY 
this.startClientY = this.startTop; 
this.MAX_LEFT = config.maxLeft||document.documentElement.clientWidth - this.moveTarget.offsetWidth; //元素可以移动的最大范围 
this.MAX_TOP = config.maxTop||document.documentElement.clientHeight - this.moveTarget.offsetHeight; 
this.lock = true; 
} 
Drag.prototype.ready = function(){ 
//绑定事件 
T.bind(document, "mousedown", repairCaller(this,this.down)); 
T.bind(document, "mousemove", repairCaller(this,this.move)); 
T.bind(document, "mouseup", repairCaller(this,this.stop)); 
} 
Drag.prototype.down = function(){ 
//取得事件对象 
var event = T.event.getEvent(arguments[0]), 
target = T.event.getTarget(event); 
if (target == this.moveTarget){ 
this.lock = false; 
//在事件开始时保存各种坐标位置 
this.startLeft = parseInt(this.moveTarget.style.left); 
this.startTop = parseInt(this.moveTarget.style.top); 
this.startClientX = event.clientX; 
this.startClientY = event.clientY; 
} 
}; 
Drag.prototype.move = function(){ 
if(!this.lock ){ 
//取得事件对象 
var event = T.event.getEvent(arguments[0]), 
target = T.event.getTarget(event); 
if(target == this.moveTarget){ 
//如有选择内容，清除之 
//window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty(); 
//凑数拖动范围有没超过最大限制 
var realLeft = this.startLeft + event.clientX - this.startClientX, //实际的移动范围 
realTop = this.startTop + event.clientY - this.startClientY, 
rightLeft , rightTop; //正确的 left, top 取值 
rightLeft = realLeft > this.MAX_LEFT ? this.MAX_LEFT : ( realLeft > 0 ? realLeft : 0 ); 
rightTop = realTop > this.MAX_TOP ? this.MAX_TOP : ( realTop > 0 ? realTop : 0 ); 
this.moveTarget.style.left = rightLeft + "px"; 
this.moveTarget.style.top = rightTop + "px"; 
} 
else{ 
this.lock = true; 
} 
} 
}; 
Drag.prototype.stop = function(){ 
this.lock = true 
};

后记：
在写的过程中非常需要注意的几点是：
1、拖动层的 position、left 和 top 必须写在 style 里
2、移动过程中设置 left 和 top 要带单位，否则不起作用
3、多级 div 嵌套时需要给父 div 加 over-flow:hidden 样式
完毕！