JavaScript 绝对定位实现回到顶部功能完整示例

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>绝对定位回到顶部按钮</title>
<style type="text/css">
body{margin:0px;padding:0px;height:2500px;background:#6f0024;}
#div1{width:120px;height:34px;right:4px;bottom:5px;cursor:pointer;background:url(images/ToTop.png) no-repeat;position:fixed;_position:absolute;display:none;}
</style>
<script type="text/javascript">
//绝对定位隐藏显示
function getScroll(id){
 var obj = document.getElementById(id);
 var timer = null;
 positionFixed(obj);
 if(obj){
 obj.style.display = 'none';
 window.onscroll=function(){
  getScrollTop() > 0 ? obj.style.display = "block" : obj.style.display = "none";
 }
 obj.onclick=function(){
  var timer = setInterval(sMove,10);
  function sMove(){
  setScrollTop(getScrollTop() / 1.5);
  if(getScrollTop() < 1)clearInterval(timer);
  }
 }
 }
}
//判断IE6
function positionFixed(obj){
 var iE6 = !-[1,] && !window.XMLHttpRequest;
 if(obj){
     var top = obj.offsetTop;
 if(iE6){
  document.documentElement.style.textOverflow = "ellipsis";
  obj.style.position = "absolute";
  obj.style.setExpression("top", "eval(documentElement.scrollTop + " + top + ') + "px"');
 }
 }
}
//获取滚动条Top
function getScrollTop(){
 return document.documentElement.scrollTop || document.body.scrollTop;
}
//回到顶部
function setScrollTop(value){
 document.documentElement.scrollTop = value;
 document.body.scrollTop = value;
}
window.onload = function(){
 getScroll('div1');
};
</script>
</head>
<body>
<div id="div1"></div>
</body>
</html>