<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript" src="js/jquery-3.2.1.min.js"></script>
<style>
* {
margin: 0;
}
.a{
background: pink;
width: 100%;
height: 1000px;
}
.b{
background: url("images/未标题-1.jpg") no-repeat;
background-position: 0px 0px;
width: 100%;
height: 420px;
background-attachment: fixed;
background-size: 100%;
}
.c{
background: #FF5B77;
width: 100%;
height: 500px;
}
</style>
</head>
<body>
<div class="a"></div>
<div class="b">
</div>
<div class="c"></div>
</body>
<script>
(function(){
var b = document.getElementsByClassName("b")[0];
//获取顶点到b的高度
var bof = b.offsetTop;//1000
window.onscroll = function(){
//获取滚动的高度
var scHeight = document.documentElement.scrollTop;
console.log(bof - scHeight);
b.style.backgroundPositionY = (bof - scHeight)*0.5 +"px";
}
})();
</script>
</html>
