页面向上向下滚动，分享到的模块随着滑动。
要点：
var scrtop =document.documentElement.scrollTop||document.body.scrollTop;
var height = document.documentElement.clientHeight||document.body.clientHeight;
var top = scrtop + (height - share.offsetHeight)/2;
top = parseInt(top);
获得页面垂直居中的位置
上代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312" />
<title>无标题文档</title>
<style>
body{margin:0; padding:0; font:12px/1.5 arial; height:2000px;}
#share{width:100px; height:200px; line-height:200px; text-align:center; border:1p solid #ccc; background:#f5f5f5; position:absolute; left:-100px; top:0;}
#share_tit{position:absolute; right:-20px; top:60px; width:20px; height:60px; padding:10px 0; background:#06c; text-align:center; line-height:18px; color:#fff;}
</style>
<script>
/*jingangel http://www.cnblogs.com/jingangel/ */
window.onload = function(){
var share = document.getElementById("share");
share.onmouseover = function(){
startrun(share,0,"left")
}
share.onmouseout = function(){
startrun(share,-100,"left")
}
window.onscroll = window.onresize = function(){
var scrtop =document.documentElement.scrollTop||document.body.scrollTop;
var height = document.documentElement.clientHeight||document.body.clientHeight;
var top = scrtop + (height - share.offsetHeight)/2;
top = parseInt(top);
startrun(share,top,"top")
}
}
var timer = null
function startrun(obj,target,direction){
clearInterval(timer);
timer = setInterval(function(){
var speed = 0;
if(direction == "left"){
speed = (target-obj.offsetLeft)/8;
speed = speed>0?Math.ceil(speed):Math.floor(speed);
if(obj.offsetLeft == target){
clearInterval(timer);
}else{
obj.style.left = obj.offsetLeft + speed + "px";
}
}
if(direction == "top"){
speed = (target-obj.offsetTop)/8;
speed = speed>0?Math.ceil(speed):Math.floor(speed);
if(obj.offsetTop == target){
clearInterval(timer);
}else{
obj.style.top = obj.offsetTop + speed + "px";
}
document.title = obj.offsetTop + ',' + target + ',' +speed;
}
},30)
}
</script>
</head>
<body>
<div id="share">
分享到内容
<span id="share_tit">分享到</span>
</div>
</body>
</html>