JavaScript 自动在表格前面增加序号

<meta http-equiv="content-type" content="text/html; charset=utf-8"> <title>javascript 自动为表格增加序号</title> <style type="text/css"> .index_tab{width:100%;border-collapse:collapse;border:1px solid #005892;margin:8px 0;} .index_tab td{line-height:35px;border:1px solid #005892;padding-left:4px;} tr.tr_top td{line-height:32px;border:none;background-color:#005892;color:#fff;font-weight:bold;} td.td_center{text-align:center;} .ys01{background-color:#e6f0fe;} </style> <table class="index_tab"> <tr class="tr_top"> <td class="td_center" width="9%">行号</td> <td width="83%">标题</td> <td class="td_center" width="11%">总计</td> </tr> <tbody id="bbstab"> <tr> <td class="td_center"></td> <td><a href="#">vc++支持窗口及文字拖放的coledroptarget扩展类</a></td> <td class="td_center">20235</td> </tr> <tr> <td class="td_center"></td> <td><a href="#">好用的ico图标截取工具vb源程序</a></td> <td class="td_center"> </td> </tr> <tr> <td class="td_center"></td> <td><a href="#">一些经典的vb加密解密算法示例</a></td> <td class="td_center"> </td> </tr> <tr> <td class="td_center"></td> <td> </td> <td class="td_center"> </td> </tr> <tr> <td class="td_center"></td> <td> </td> <td class="td_center"> </td> </tr> <tr> <td class="td_center"></td> <td> </td> <td class="td_center"> </td> </tr> </tbody> </table>
[ctrl+a 全选 注:如需引入外部js需刷新才能执行]