介绍一个比较简单的返回顶部代码，可以用图片代替“返回顶部”

<script>
lastScrollY=0;
function heartBeat(){
var diffY;
if (document.documentElement && document.documentElement.scrollTop)
    diffY = document.documentElement.scrollTop;
else if (document.body)
    diffY = document.body.scrollTop
else
    {/*Netscape stuff*/}
percent=.1*(diffY-lastScrollY);
if(percent>0)percent=Math.ceil(percent);
else percent=Math.floor(percent);
document.getElementById("full").style.top=parseInt(document.getElementById("full").style.top)+percent+"px";
lastScrollY=lastScrollY+percent;
}
suspendcode="<div id=\"full\" style='right:1px;POSITION:absolute;TOP:600px;z-index:100'><a onclick='window.scrollTo(0,0);'>返回顶部</a><br></div>"
document.write(suspendcode);
window.setInterval("heartBeat()",1);
<script>