就像这种我只想遍历第一个TR里面的第三个TD,应该怎么做
<TABLE id="tb1">
<TR>
<TD>a</TD>
<TD>b</TD>
<TD>c</TD>
</TR>
<TR>
<TD>A</TD>
<TD>B</TD>
<TD>C</TD>
</TR>
<TR>
<TD>1</TD>
<TD>2</TD>
<TD>3</TD>
</TR>
</TABLE>
<script language="javascript">
var tb1=document.getElementById("tb1");
for(i=0;i<tb1.rows.length;i++){
alert(tb1.rows[i].cells[1].innerText);
}
</script>
<TABLE id="tb1">
<TR>
<TD>a</TD>
<TD>b</TD>
<TD>c</TD>
</TR>
<TR>
<TD>A</TD>
<TD>B</TD>
<TD>C</TD>
</TR>
<TR>
<TD>1</TD>
<TD>2</TD>
<TD>3</TD>
</TR>
</TABLE>
<script language="javascript">
var tb1=document.getElementById("tb1");
for(i=0;i<tb1.rows.length;i++){
alert(tb1.rows[i].cells[1].innerText);
}
</script>
<tr onmouseover="alert(this.cells[7].innerHTML);">
<td>aaaaa</td>
<td>bbbbb</td>
<td>ccccc</td>
<td>ddddd</td>
<td>eeeee</td>
<td>fffff</td>
<td>ggggg</td>
<td>hhhhh</td>
</tr>
</table>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script language="javascript">
function show_text(obj_id,i) //i为想要显示的单元格索引
{
alert(obj_id.childNodes[i].lastChild.nodeValue);
}
</script>
</head><body>
<table width="800" border="1">
<tr onmouseover="show_text(this,7)">
<td width="100">1 </td>
<td width="100">2 </td>
<td width="100">3 </td>
<td width="100">4 </td>
<td width="100">5 </td>
<td width="100">6 </td>
<td width="100">7 </td>
<td width="100">8 </td>
</tr>
</table>
</body>
</html>