<!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>
</head>
<body style="height:2000px">
<div style="margin-top:1000px;overflow: hidden;">
<div id="demo" style=" 500px;height: 300px; background-color: red;transition: all 1s; opacity: 0.1;"></div>
</div>
</body>
</html>
<script src="https://code.jquery.com/jquery-2.2.4.min.js"
integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44=" crossorigin="anonymous"></script>
<script>
$(window).scroll(function (e) {
//元素
var demo = $("#demo");
//滚动条滚动的高度
var scrollTop = $(document).scrollTop();
//浏览器可视化区域的高度
var docHeight = $(window).height();
//滚动最小位置，开始动画
var mintop = demo.offset().top + demo.height() - docHeight;
//滚动最大位置，开始动画
var maxtop = demo.offset().top;
//在一定范围内，开始过度动画，出了范围，就将过度动画还原为未执行时的样式
if(mintop <= scrollTop && maxtop >= scrollTop){
//开始动画
demo.css({
"opacity":1,
"margin-left":"500px"
})
}
else{
//还原动画
demo.css({
"opacity":0.1,
"margin-left":"0px"
})
}
});
</script>