<!DOCTYPE html>
<html>
<head>
<meta charset=" utf-8">
<meta name="author" content="https://www.jb51.net/" />
<title>脚本之家</title>
<style type="text/css">
span{color:red;}
</style>
<script type="text/javascript" src="mytest/jQuery/jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function(){
$("#btn").click(function(){
$("span").text($("li").size());
})
})
</script>
</head>
<body>
<div>
<ul>
<li>后台专区</li>
<li>前台专区</li>
<li>数据库专区</li>
<li>站长交流</li>
</ul>
</div>
<div>li元素集合中li元素的数量:<span></span></div>
<button id="btn">点击查看实例</button>
</body>
</html>