<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>对联广告</title>
<style>
* {
margin: 0;
padding: 0;
}
.left {
float: left;
position: fixed;
top: 150px;
left: 0;
}
.right {
float: right;
position: fixed;
top: 150px;
right: 0;
}
img {
display: none;
}
</style>
<script src="./js/jquery-3.5.1.js"></script>
<script>
$(function () {
// 监听网页的滚动
$(window).scroll(function () {
// 获取网页滚动的偏移量
const offset = $("html, body").scrollTop()
// 当网页滚动到该位置，显示广告
if (offset >= 250) {
$("img").show(1000);
} else {
// 当网页回滚时，隐藏广告
$("img").hide(1000)
}
})
})
</script>
</head>
<body>
<img src="images/ad.png" alt="" class="left">
<img src="images/ad.png" alt="" class="right">
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</body>
</html>
jQuery实例——对联广告 
![跨域方案简单介绍[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)