W3School TIY
编辑您的代码：
<html> <head> <script type="text/javascript" src="../jquery/jquery.js"></script> <script type="text/javascript"> $(document).ready(function(){ $("button").click(function(){ $("p:first").addClass("intro"); }); }); </script> <style type="text/css"> .intro { font-size:120%; color:red; } </style> </head> <body> <h1>This is a heading</h1> <p>This is a paragraph.</p> <p>This is another paragraph.</p> <button>向第一个 p 元素添加一个类</button> </body> </html>
查看结果: