怎么让两个TR可以颠倒位置

Question

http://lucky.myrice.com/javascriptexam/sortRow.htm

Answer 1

<table border="1" width="100" id=s>
  <tr>
    <td width="50%">1</td>
    <td width="50%">2</td>
  </tr>
  <tr>
    <td width="50%">3</td>
    <td width="50%">5</td>
  </tr>
  <tr>
    <td width="50%">6</td>
    <td width="50%">7</td>
  </tr>
</table>
<input type="button" value="Down" onclick="s.insertRow(0).replaceNode(s.rows[s.rows.length-1])">
<input type="button" value=" Up "onclick="s.insertRow(s.rows.length).replaceNode(s.rows[0])">

Answer 2

<table><tr><td>
<table id="tb1" border=1>
   <tr><td>aaa</td></tr>
    <tr><td>aaa</td></tr>
</table>
</td></tr><tr><td>
<table id="tb2" border=1>
   <tr><td>bbb</td></tr>
   <tr><td>bbb</td></tr>
</table>
</td></tr>
</table>
<INPUT TYPE = button VALUE = "Swap List" onclick = "fnSwap()">
<SCRIPT>
function fnSwap(){
   tb1.swapNode(tb2);
}
</SCRIPT>