页面向上向下滚动，分享到的模块随着滑动。
要点：
代码如下:
var scrtop =document.documentelement.scrolltop||document.body.scrolltop;
var height = document.documentelement.clientheight||document.body.clientheight;
var top = scrtop + (height - jb51.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;}
#jb51{width:100px; height:200px; line-height:200px;
text-align:center; border:1p solid #ccc;
background:#f5f5f5; position:absolute; left:-100px; top:0;}
#jb51_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>
window.onload = function(){
var jb51 = document.getelementbyid(jb51);
jb51.onmouseover = function(){
startrun(jb51,0,left)
}
jb51.onmouseout = function(){
startrun(jb51,-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 - jb51.offsetheight)/2;
top = parseint(top);
startrun(jb51,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=jb51>
分享到内容
<span id=jb51_tit>分享到</span>
</div>
</body>
</html>
