高手请看看为什么这样不行,应该怎么写?先谢!
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>无标题文档</title>
</head>
<script language="JavaScript" type="text/JavaScript">
function add(){
window.alert(document.all.at.innerHTML);
document.all.at.innerHTML=document.all.at.innerHTML+"<tr><td>222</td></tr>";
window.alert(document.all.at.innerHTML);
}
</script>
<body>
<table width="100%" border="1" cellspacing="0" cellpadding="0">
<span id="at">
<tr>
<td>111</td>
</tr>
</span>
</table>
<input name="add" value="add" type="button" onClick="add();">
</body>
</html>