<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title></title> </head> <body> <a href="#" title="你好" class="red" id="app">黑马程序员</a> </body> <!--以下两种方式等价: 即<script></script>和<script type="text/javascript"></script>方式等价 --> <!--<script></script>--> <script type="text/javascript"> var oApp = document.getElementById("app") // 修改class属性值 oApp.className="black" </script> </html> <!-- 修改类属性值 -->