仿CSDN Blog返回页面顶部功能实现原理及代码

<div id="d-" style="display:none;">
<a id="d--a" href="#" title="回到顶部">
<img src="http://static.blog.csdn./images/.png" alt="TOP" /></a>
</div>

<script type="text/javascript">
$(function(){
var d_=$('#d-');
document.onscroll=function(){
var scrTop=(document.body.scrollTop||document.documentElement.scrollTop);
if(scrTop>500){
if(scrTop>0){
d_.show();
}else{
d_.hide();
}
}
$('#d--a').click(function(){
$("html,body").animate({scrollTop: 0},500);
//scrollTo(0,0);
this.blur();
return false;
});
});
</script>

#d- {
position: fixed;
float: right;
z-index: 10;
right: 10px;
bottom: 40px;
}
#d- img {
width: 42px;
opacity: 0.3;
}
img {
border: medium none;
}