<!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>