jquery版楼层滚动特效

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>楼层滚动特效</title>
</head>
<script src="js/jquery-1.9.1.min.js" type="text/javascript" charset="utf-8"></script>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
#F1{
width:100%;
height: 500px;
background-color: #00008B;
}
#F2{
width:100%;
height: 500px;
background-color: #00FF00;
}
#F3{
width:100%;
height: 500px;
background-color: #00FFFF;
}
#F4{
width:100%;
height: 500px;
background-color: #1AC78C;
}
#F5{
width:100%;
height: 500px;
background-color: #6495ED;
}
#ulbox{
position: fixed;
left:30px;
top:25%;
}
#ulbox li{
list-style: none;
width: 50px;
height: 50px;
line-height: 50px;
text-align: center;
border: 1px solid #000;
background-color: #fff;
}
a{
display: block;
text-decoration: none;
cursor: pointer;
}
.current{
background-color: #FF0000;
}
</style>
<body>
<div id="content">
<div id="F1" class="item">
楼层一
</div>
<div id="F2" class="item">
楼层二
</div>
<div id="F3" class="item">
楼层三
</div>
<div id="F4" class="item">
楼层四
</div>
<div id="F5" class="item">
楼层五
</div>
</div>
<ul id='ulbox'>
<li><a href="#F1" class="current">F1</a></li>
<li><a href="#F2">F2</a></li>
<li><a href="#F3">F3</a></li>
<li><a href="#F4">F4</a></li>
<li><a href="#F5">F5</a></li>
</ul>
</body>
<script type="text/javascript">
$(document).ready(function(){
$(window).scroll(function(){
var top=$(document).scrollTop();
var ulbox=$('#ulbox');
var items=$('#content').find('.item');
var currentId='';//当前所在楼层的#id
items.each(function(){
var _this=$(this);
var itemstop=_this.offset().top;//遍历出每个楼层距离顶部的高度
if(top>itemstop-200){
currentId='#'+_this.attr('id');
}else{
return false;
}
})
var currentLink=ulbox.find('.current');
if(currentId&&currentLink.attr('href')!=currentId){
currentLink.removeClass('current');
ulbox.find('[href='+currentId+']').addClass('current');
}
});

});

</script>
</html>