<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style>
#div1{
100px;
height:150px;
background:red;
position:absolute;
right:0;
bottom:0;
}
</style>
<script>
window.onscroll=function (){
var oDiv=document.getElementById('div1');
var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;//做兼容
startMove(parseInt((document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop));//使用parseInt是防止可能出现除2之后出现.5情况，导致悬浮框上下抖动。
};
var timer=null;
function startMove(iTarget)
{
var oDiv=document.getElementById('div1');
clearInterval(timer);
timer=setInterval(function (){
var speed=(iTarget-oDiv.offsetTop)/4;
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if(oDiv.offsetTop==iTarget)
{
clearInterval(timer);
}
else
{
document.getElementById('txt1').value=oDiv.offsetTop;
oDiv.style.top=oDiv.offsetTop+speed+'px';
}
},30);
}
</script>
</head>
<body style="height:2000px;" >
<input type="text" id="txt1" style="position:fixed; right:0; top:0;"/>
<div id="div1"></div>
</body>
</html>效果图：
