<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<style>
#bot {
position: fixed;
right: 50px;
bottom: 100px;
background: red;
color: #fff;
text-decoration: none;
display: none;
}
</style>
<body>
<script>
</script>
<div style="width: 100%;height: 200px;background: red;">111</div>
<div style="width: 100%;height: 200px;background: blueviolet;">111</div>
<div style="width: 100%;height: 200px;background: bisque;">111</div>
<div style="width: 100%;height: 200px;background: teal;">111</div>
<div style="width: 100%;height: 200px;background: tomato;">111</div>
<div style="width: 100%;height: 200px;background: red;">111</div>
<div style="width: 100%;height: 200px;background: blueviolet;">111</div>
<div style="width: 100%;height: 200px;background: bisque;">111</div>
<div style="width: 100%;height: 200px;background: teal;">111</div>
<div style="width: 100%;height: 200px;background: tomato;">111</div>
<div style="width: 100%;height: 200px;background: red;">111</div>
<div style="width: 100%;height: 200px;background: blueviolet;">111</div>
<div style="width: 100%;height: 200px;background: bisque;">111</div>
<div style="width: 100%;height: 200px;background: teal;">111</div>
<div style="width: 100%;height: 200px;background: tomato;">111</div>
<div style="width: 100%;height: 200px;background: red;">111</div>
<div style="width: 100%;height: 200px;background: blueviolet;">111</div>
<div style="width: 100%;height: 200px;background: bisque;">111</div>
<div style="width: 100%;height: 200px;background: teal;">111</div>
<div style="width: 100%;height: 200px;background: tomato;">111</div>
<a href="javascript:;" id="bot" title="返回顶部">返回顶部</a>
</body>
<script type="text/javascript">
var dsq = null;
bot.onclick = function() {
dsq = setInterval(function() {
var gaodu = document.body.scrollTop || document.documentElement.scrollTop;
var sudu = Math.floor(-gaodu / 5);
document.body.scrollTop = document.documentElement.scrollTop = gaodu + sudu;
if(gaodu == 0) {
clearInterval(dsq);
}
}, 30);
}
window.onscroll = function() {
if(document.documentElement.scrollTop + document.body.scrollTop > 0) {
bot.style.display = "block";
} else {
bot.style.display = "none";
}
}
</script>
</html>