<html>
<head>
<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$("button").click(function(){
alert($("li").length);
});
});
</script>
</head>
<body>
<button>Alert the number of li elements</button>
<ul>
<li>Coffee</li>
<li>Milk</li>
<li>Soda</li>
</ul>
</body>
</html>