table的子节点问题，这个table的子节点问什么只有2个？
<!DOCTYPE html>
<html>
<head>
<title> new document </title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
</head>
<body>
<table border="1" width="50%" id="table">
<tr>
<th>学号</th>
<th>姓名</th>
<th>操作</th>
</tr>
<tr>
<td>xh001</td>
<td>王小明</td>
<td><a href="javascript:;" onclick="deleteRow(this)">删除</a></td>
</tr>
<tr>
<td>xh002</td>
<td>刘小芳</td>
<td><a href="javascript:;" onclick="deleteRow(this)">删除</a></td>
</tr>
</table>
<script type="text/javascript">
var mytr=document.getElementById("table").childNodes;
document.write(mytr.length);
</script>
</body>
</html>
