<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
#div{
200px;
height: 100px;
background: red;
position: absolute;
right: 0;
bottom: 40%;
}
</style>
<script>
window.onscroll = function () {
var oDiv = document.getElementById('div');
var scrollTop = document.documentElement.scrollTop||document.body.scrollTop;
//oDiv.style.top = (document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop+'px';
startMove(parseInt((document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop));
};
var time = null;
function startMove(iTarget){
var oDiv = document.getElementById('div');
clearInterval(time);
time = setInterval(function(){
var speed = (iTarget-oDiv.offsetTop)/6;
speed = speed>0?Math.ceil(speed):Math.floor(speed);
if(oDiv.offsetTop == iTarget){
clearInterval(time)
}else{
oDiv.style.top = oDiv.offsetTop+speed+'px';
}
},30)
}
</script>
</head>
<body style="height: 2000px;">
<div id="div"></div>
</body>
</html>