<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">
<title>回到顶部效果（原生js）</title>
<style type="text/css">
body{
margin: 0;
}
.bg{
width: 1022px;
margin: 0 auto;
}
.btn{
display: none;
width: 75px;
height: 75px;
background:url(../images/网页top小图标（返回顶部）/返回顶部-085.png) no-repeat left top;
position: fixed;
left: 50%;
margin-left: 530px;
bottom: 10px;
text-indent: -9999px;
outline: none;
}
.btn:hover{
background-position: 0 -75px;
}
</style>
<script>
var timer=null;
var isScroll=true;
//1.2构造oScroll函数
function oScroll(){
var osTop=document.documentElement.scrollTop||document.body.scrollTop;//1.1滚动高度,兼容
var oSpeed=Math.ceil(osTop/4);//滚动速度
document.documentElement.scrollTop=document.body.scrollTop=osTop-oSpeed;
if(osTop==0){//判断到达顶部,清理定时器
clearInterval(timer);
}
isScroll=true;
}
window.onload=function() {
var obtn=document.getElementById('btn');//获取按钮元素
var clientHeight=document.documentElement.clientHeight||document.body.clientHeight;
// 1.点击返回按钮事件
btn.onclick=function(){//为按钮绑定点击事件
timer=setInterval(oScroll,50);
}
window.onscroll=function() {
var osTop=document.documentElement.scrollTop||document.body.scrollTop;//1.1滚动高度,兼容
if (osTop>clientHeight) {
btn.style.display="block";
}else{
btn.style.display="none";
}
if(!isScroll){
clearInterval(timer);
}
isScroll=false;
}
}
</script>
</head>
<body>
<div class="bg">
<img src="../images/jz.jpg">
</div>
<a href="javascript:void(0);" title="返回顶部" id="btn" class="btn">返回顶部</a>
</body>
</html>
