源代码:
<!DOCTYPE html> <html> <head> <script src="http://libs.baidu.com/jquery/1.10.2/jquery.min.js"> </script> <script> $(document).ready(function(){ $("button").click(function(){ $("p:first").addClass("intro"); }); }); </script> <style> .intro { font-size:150%; color:red; } </style> </head> <body> <h1>This is a heading</h1> <p>This is a paragraph.</p> <p>This is another paragraph.</p> <button>Add a class name to the first p element</button> </body> </html>
运行结果：