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实现效果：
分析：
1.当鼠标在粉色div上按下时，捕获onmousedown事件，获取鼠标的坐标clientX,clientY
2.鼠标在按下后移动，整个div跟随着移动，获取鼠标按下时相对于整个div的坐标，即下图中的disx,dixy
3.鼠标抬起后，整个div不再随鼠标移动，onmouseup事件
4.设置整个div能够活动的范围，即浏览器窗口大小减去div本身所占大小
具体代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title></title>
<style type="text/css">
body{margin:0;padding:0;}
#wrap{width:300px;height:200px;border:1px solid #FFFFCC;background-color:#CCFFFF;position:absolute;}
#moveHere{cursor: move;width:300px;height: 30px;text-align: center;line-height:30px;background-color:#FFCCCC;}
</style>
</head>
<body>
<div id="wrap">
<div id="moveHere"></div>
</div>
<script type="text/javascript">
var moveHere=document.getElementById("moveHere");
var wrap=document.getElementById("wrap");
var winW=document.documentElement.clientWidth || document.body.clientWidth;
var winH=document.documentElement.clientHeight || document.body.clientHeight;
maxW=winW-wrap.offsetWidth;
maxH=winH-wrap.offsetHeight;
window.onload=function(){
wrap.style.left=(maxW/2)+"px";
wrap.style.top=(maxH/2)+"px";
moveHere.onmousedown=mousedown;
moveHere.onmouseup=mouseup;
}
function mousedown(event){
event=event||window.event;
var disx = event.clientX-wrap.offsetLeft;
var disy = event.clientY-wrap.offsetTop;
document.onmousemove = function(event){
event=event||window.event;
move(event,disx,disy);
}
}
function move(event,disx,disy){
var x = event.clientX-disx;
var y = event.clientY-disy;
if(x<0){
x=0;
}else if(x>maxW){
x=maxW;
}
if(y<0){
y=0;
}else if(y>maxH){
y=maxH;
}
wrap.style.left=x+"px";
wrap.style.top=y+"px";
}
function mouseup(){
document.onmousemove=null;
document.onmouseup=null;
}
</script>
</body>
</html>