jquery实现返回页面顶部功能。

<p id="back-to-top">
<span></span>
</p>

<script type="text/javascript">
$(function() {
//首先将#back-to-top隐藏
$("#back-to-top").hide();
//当滚动条的位置处于距顶部100像素以下时，跳转链接出现，否则消失
$(function() {
$(window).scroll(function() {
if ($(window).scrollTop() > 100) {
$("#back-to-top").fadeIn(1500);
} else {
$("#back-to-top").fadeOut(1500);
}
});
//当点击跳转链接后，回到页面顶部位置
$("#back-to-top").click(function() {
$('body,html').animate({
scrollTop : 0
}, 300);
return false;
});
});
});
</script>

<style type="text/css">
p#back-to-top {
position: fixed;
bottom: 100px;
right: 80px;
cursor:pointer;
}

p#back-to-top  span {
background:url(skins/images/totop.gif) no-repeat center center;
border-radius: 6px;
display: block;
height: 80px;
width: 80px;
margin-bottom: 5px;
/*使用CSS3中的transition属性给<span>标签背景颜色添加渐变效果*/
-moz-transition: background 1s;
-webkit-transition: background 1s;
-o-transition: background 1s;
}

#back-to-top span:hover {
background: url(skins/images/totop.gif) no-repeat center center;
}
</style>