<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>shangxia</title>
<style>
*{margin: 0;padding: 0;}
#div1 {width:100px; height:100px; background:red; position:absolute; right:0;}
</style>
<script>
window.onload = function(){
var oDiv = document.getElementById('div1');
var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
var t=scrollTop+(document.documentElement.clientHeight-oDiv.offsetHeight)/2;
var timer = 0;
starMove (100)
function starMove (target){
clearInterval(timer)
timer = setInterval(function(){
var speed=(target-oDiv.offsetTop)/8;
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if (oDiv.offsetTop==target) {
clearInterval(timer)
}else{
oDiv.style.top=oDiv.offsetTop+speed+'px';
};
txt1.value=oDiv.offsetTop+',目标：'+target;
},30)
}
}
</script>
</head>
<body style="height:2000px;">
<input id="txt1" type="text" style="position:fixed; top:20px;" />
<div id="div1"></div>
</body>
</html>下来的时候Div不会跟随滚动条移动，问题出在哪里，而且怎么样让下拉默认位置Div居中。