<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>jq之demo</title><!--线上jq库--><script src="https://code.jquery.com/jquery-3.4.1.min.js"></script><script>$(document).ready(function(){$("button").click(function(){/*$("ul li:first-child")指定每个ul的第一个li元素*/$("ul li:first-child").hide();});});</script>
</head>
<body>
<p>List 1:</p>
<ul><li>Coffee</li><li>Milk</li><li>Tea</li>
</ul>
<p>List 2:</p>
<ul><li>Coffee</li><li>Milk</li><li>Tea</li>
</ul>
<button>点我</button>
</body>
</html>