<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>仿淘宝滚动侧边栏</title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
.w{
width:1600px;
margin:10px auto 0px auto;
}
.header{
height:200px;
background: pink;
}
.banner{
height:500px;
background: purple;
}
.main{
height:1500px;
background:cornflowerblue;
}
.slyder-bar{
position: relative;
float: right;
top:600px;
right:98px;
width:50px;
height:200px;
background:pink;
}
.goback{
display: inline-block;
text-align: center;
line-height: 20px;
width:40px;
height: 40px;
bottom:0px;
position: absolute;
}
</style>
</head>
<body>
<div class="slyder-bar">
<span class="goback">返回顶部</span>
</div>
<div class="header w">header</div>
<div class="banner w">banner</div>
<div class="main w">main</div>
<script type="text/javascript">
var slyderbar=document.querySelector('.slyder-bar')
var banner=document.querySelector('.banner');
var bannerTop=banner.offsetTop;
var slyderbarTop=slyderbar.offsetTop-bannerTop;
var main=document.querySelector('.main');
var goback=document.querySelector('.goback');
var mainTop=main.offsetTop;
document.addEventListener('scroll',function(){
if(window.pageYOffset>=bannerTop){
slyderbar.style.position='fixed';
slyderbar.style.top=slyderbarTop+'px';
}else{
slyderbar.style.position="absolute";
slyderbar.style.top='600px';
}
if(window.pageYOffset>=mainTop){
goback.style.display="block";
}else{
goback.style.display="none";
}
})
</script>
</body>
</html>
