<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
body{
height: 10000px;
}
.shadow{
height: 100%;
overflow: hidden;
}
</style>
</head>
<body id="body">
<div class="btn1">点击</div>
<div class="btn2">停止</div>
<script src="jquery-1.11.3.min.js"></script>
<script>
$('.btn1').click(function(){
$('body').addClass('shadow');
})
$('.btn2').click(function(){
$('body').removeClass('shadow');
})
</script>
</body>
</html>
实现原理：
给body设置属性overflow:hidden;height:100%;
