js在html页面回到顶部的做法

效果图

 先引入js

<script type="text/javascript" src="${contextPath}js/common/returnTop.js"></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:2px;POSITION:absolute;TOP:600px;z-index:100'><a onclick='window.scrollTo(0,0);'><img src='../img/www/top.png'></img></a><br></div>"
document.write(suspendcode);
window.setInterval("heartBeat()",1);