复制代码 代码如下:
/*
*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！