如何得到表格的最后一个td的id

Question

tablename.rows[tablename.rows.length-1].cells[tablename.rows[tablename.rows.length-1].length-1].id

Answer 1

<TABLE id="bb">
<TR>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR>
<TD></TD>
<TD></TD>
<TD id="aa"></TD>
</TR>
</TABLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
var tr_num=bb.childNodes(0).childNodes.length-1; 
var td_num=bb.childNodes(0).childNodes(tr_num).childNodes.length-1;
alert(bb.childNodes(0).childNodes(tr_num).childNodes(td_num).id)
//-->
</SCRIPT>

Answer 2

tableName.lastChild.lastChild.lastChild.id