效果：
HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>拖拽库靠谱</title>
<style type="text/css">
div,h2,p{margin:0;padding:0}
body{font:14px/1.5 arial}
#box{width:300px;height:100px;background:#fef4eb;padding:5px;border:1px solid #666}
#box #title{height:25px;background:#ccc;display:inline-block;cursor:move;width:100%;text-align:center}
.content{text-align:center;line-height:50px}
</style>
</head>
<body>
<div id="box">
<span id="title">按下拖拽</span>
<div class='content'>内容区</div>
</div>
<script src='drag.js'></script>
<script type="text/javascript">
//应用
var oBox = document.getElementById("box");
var oTitle = document.getElementById("title");
var oDrag = new Drag(oBox, {handle:oTitle, limit:false});
</script>
</body>
</html>
drag.js：
function Drag(){
//初始化
this.initialize.apply(this, arguments)
}
Drag.prototype = {
//初始化
initialize : function (drag, options){
this.drag = this.$(drag);
this._x = this._y = 0;
this._moveDrag = this.bind(this, this.moveDrag);
this._stopDrag = this.bind(this, this.stopDrag);
this.setOptions(options);
this.handle = this.$(this.options.handle);
this.maxContainer = this.$(this.options.maxContainer);
this.maxTop = Math.max(this.maxContainer.clientHeight, this.maxContainer.scrollHeight) - this.drag.offsetHeight;
this.maxLeft = Math.max(this.maxContainer.clientWidth, this.maxContainer.scrollWidth) - this.drag.offsetWidth;
this.limit = this.options.limit;
this.lockX = this.options.lockX;
this.lockY = this.options.lockY;
this.lock = this.options.lock;
this.onStart = this.options.onStart;
this.onMove = this.options.onMove;
this.onStop = this.options.onStop;
this.handle.style.cursor = "move";
this.changeLayout();
this.addHandler(this.handle, "mousedown", this.bind(this, this.startDrag))
},
changeLayout : function (){
this.drag.style.top = this.drag.offsetTop + "px";
this.drag.style.left = this.drag.offsetLeft + "px";
this.drag.style.position = "absolute";
this.drag.style.margin = "0"
},
startDrag : function (event){
var event = event || window.event;
this._x = event.clientX - this.drag.offsetLeft;
this._y = event.clientY - this.drag.offsetTop;
this.addHandler(document, "mousemove", this._moveDrag);
this.addHandler(document, "mouseup", this._stopDrag);
event.preventDefault && event.preventDefault();
this.handle.setCapture && this.handle.setCapture();
this.onStart()
},
moveDrag : function (event){
var event = event || window.event;
var iTop = event.clientY - this._y;
var iLeft = event.clientX - this._x;
if (this.lock) return;
this.limit && (iTop < 0 && (iTop = 0), iLeft < 0 && (iLeft = 0), iTop > this.maxTop && (iTop = this.maxTop), iLeft > this.maxLeft && (iLeft = this.maxLeft));
this.lockY || (this.drag.style.top = iTop + "px");
this.lockX || (this.drag.style.left = iLeft + "px");
var iWinWidth = document.documentElement.clientWidth;
var iWinHeight = document.documentElement.clientHeight;
if(this.drag.offsetLeft<0){
this.drag.style.left =0+'px';
}else if(this.drag.offsetLeft>(iWinWidth-this.drag.offsetWidth)){
this.drag.style.left =iWinWidth-this.drag.offsetWidth+'px';
}
if(this.drag.offsetTop<0){
this.drag.style.top =0+'px';
}else if(this.drag.offsetTop>(iWinHeight-this.drag.offsetHeight)){
this.drag.style.top =iWinHeight-this.drag.offsetHeight+'px';
}
event.preventDefault && event.preventDefault();
this.onMove()
},
stopDrag : function (){
this.removeHandler(document, "mousemove", this._moveDrag);
this.removeHandler(document, "mouseup", this._stopDrag);
this.handle.releaseCapture && this.handle.releaseCapture();
this.onStop()
},
//参数设置
setOptions : function (options){
this.options ={
handle: this.drag, //事件对象
limit: true, //锁定范围
lock: false, //锁定位置
lockX: false, //锁定水平位置
lockY: false, //锁定垂直位置
maxContainer: document.documentElement || document.body, //指定限制容器
onStart: function () {}, //开始时回调函数
onMove: function () {}, //拖拽时回调函数
onStop: function () {} //停止时回调函数
};
for (var p in options) this.options[p] = options[p]
},
//获取id
$ : function (id)
{
return typeof id === "string" ? document.getElementById(id) : id
},
//添加绑定事件
addHandler : function (oElement, sEventType, fnHandler)
{
return oElement.addEventListener ? oElement.addEventListener(sEventType, fnHandler, false) : oElement.attachEvent("on" + sEventType, fnHandler)
},
//删除绑定事件
removeHandler : function (oElement, sEventType, fnHandler)
{
return oElement.removeEventListener ? oElement.removeEventListener(sEventType, fnHandler, false) : oElement.detachEvent("on" + sEventType, fnHandler)
},
//绑定事件到对象
bind : function (object, fnHandler)
{
return function ()
{
return fnHandler.apply(object, arguments)
}
}
};