<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>jq3</title>
<style>
.back{
position: fixed;
right: 0px;
bottom: 0px;
}
.heid{
display: none;
}
</style>
</head>
<body>
<div style="height: 2000px"></div>
<div id ='ck' onclick="gotop()" class="back heid">GotoTop</div>
<script type="text/javascript" src="jquery-2.2.4.js"></script>
<script type="text/javascript">
function gotop(){
$(window).scrollTop(0)
}
$(function(){
$(window).scroll(function(){
var top=$(window).scrollTop()
if (top > 100){
$('#ck').removeClass('heid')
}else{
$('#ck').addClass('heid')
}
});
});h
</script>
</body>
</html>
