<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title></title> <script src="js/JQ3.3.1.js"></script> <link rel="stylesheet" type="text/css" href="css/style.css"/> <script type="text/javascript"> $(function(){//对div添加txt的样式 $(showMsg).attr("class","txt");//所有div都会有效果，其中txt是css中定义的样式 //$("#showMsg").attr("class","txt");//一次只会选中第一个div }) </script> </head> <body> <div id="showMsg"><h1>test</h1></div> <div id="showMsg"><h1>test</h1></div> <span>test</span> <span>test</span> <p>test</p> <p>test</p> </body> </html>