getElementsByTagName疑问

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你把 html标签和 javascript脚本换个位置试试 js拿到下面来
<body>
<table id="te" width="699" border="1" cellpadding="0" cellspacing="0" align="center">
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
</table>
</body>
<script language="javascript">
var arr=document.getElementsByTagName('table');
var x=arr.getElementsByTagName("td");alert(x.length);
var tdvalue=new Array("电视剧","电影","动漫","日韩电视剧","武林外传","色戒","柯南","爱在哈佛","天龙八部","英雄","蜡笔小新","金三顺","射雕英雄传","天下无贼","灌篮高手","浪漫满屋");
var tdnode =new Array();
var i;
for(i=0;i<x.length;i++)
{
tdnode[i]=document.createTextNode(tdvalue[i]);
x[i].appendChild(tdnode[i]);
}
</script>
<table id="te" width="699" border="1" cellpadding="0" cellspacing="0" align="center">
  <tr>
  <td id="x"> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
  <tr>
  <td> </td>
  <td> </td>
  <td> </td>
  <td> </td>
  </tr>
</table><script language="javascript">
var arr=document.getElementsByTagName('table')[0];
var x=arr.getElementsByTagName("TD");
alert(x.length);
var tdvalue=new Array("电视剧","电影","动漫","日韩电视剧","武林外传","色戒","柯南","爱在哈佛","天龙八部","英雄","蜡笔小新","金三顺","射雕英雄传","天下无贼","灌篮高手","浪漫满屋");
var tdnode =new Array();
var i;
for(i=0;i<x.length;i++)
{
tdnode[i]=document.createTextNode(tdvalue[i]);
x[i].appendChild(tdnode[i]);
}
</script>
但是还是获取不了td的数量，table数量可以了
document.getElementsByTagName 获得的是个数组var arr=document.getElementsByTagName('table')[0];
这样就行了
注意，你的JS代码在执行的时候，可能页面还没有加载完毕
所以，加上window.onload再试试看
另外，关于document.getElementsByTagName还是少用为妙，请看这个帖子：【分享】深入挖掘document.getElementsByTagName()方法的返回值