问一个表格的问题。

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Display Test</title>
<meta http-equiv="Content-Type" content="text/html; charset=Shift_JIS">
<script language="JavaScript">
function ExpandAll()
{var i = 1;
var j = 1;
var targetTR = 'TRGroupCode' + '_' + i ;
var targetTD = 'TDGroupCode' + '_' + i ;
while(j==1)
{
try
{
var objTR =eval(targetTR);
var objTD =eval(targetTD);
if (objTR!=null)
{
if(document.all('chkExpandAll').checked == true)
{
Expand(targetTR,'ExpandAll');
document.all(targetTD).innerHTML = "-" ;
}
else
{
Expand(targetTR,'UnExpandAll');
document.all(targetTD).innerHTML = "+" ;
}
i = i + 1;
targetTR = 'TRGroupCode' + '_' + i ;
targetTD = 'TDGroupCode' + '_' + i ;
}
else
{
j = 0 ;
return ;
}
}
catch(e)
{
j = 0 ;
if(document.all('chkExpandAll').checked == true)
{
document.all('chkExpandAll').checked == false;
}
else
{
document.all('chkExpandAll').checked == true;
} return ;
}
}
}function Expand(targetTR,targetTD){var i = 1;
var j = 1;
var SecondtargetTR = targetTR + '_' + i ;
//alert(targetTR);
while(j==1)
{
try{
var obj =eval(SecondtargetTR);
if (obj!=null)
{
if(targetTD == 'ExpandAll')
{
obj.style.display = "block";
}
else 
{
if(targetTD == 'UnExpandAll')
{
obj.style.display = "none";
}
else
{
if(obj.style.display == "none")
{
obj.style.display = "block";
document.all(targetTD).innerHTML = "-";
}
else
{
obj.style.display = "none";
document.all(targetTD).innerHTML = "+";
}
}
}
i = i + 1;
SecondtargetTR = targetTR + '_' + i ;
}
else
{
j = 0 ;
return ;
}
}
catch(e)
{
j = 0 ;
return ;
}
}}</script>
</head><body>
<table width="75%" border="1">
  <tr>
    <td id="tdExpandAll">全展<input type="checkbox" onClick="ExpandAll()" id="chkExpandAll"></td>
    <td>Group1</td>
    <td>Group3</td>
  </tr>
  <tr id="TRGroupCode_1" bgcolor="#FFCCBB">
    <td  onClick="Expand('TRGroupCode_1','TDGroupCode_1')" id="TDGroupCode_1">+</td>
    <td>1_1</td>
    <td>1_2</td>
  </tr>
  <tr  id="TRGroupCode_1_1" style="display:none" bgcolor="#CCCCCC">
    <td>1_1</td>
    <td>1_1</td>
    <td>1_1</td>
  </tr>
  <tr  id="TRGroupCode_1_2" style="display:none" bgcolor="#CCCCCC">
    <td>1_2</td>
    <td>1_2</td>
    <td>1_2</td>
  </tr>
  <tr id="TRGroupCode_2" bgcolor="#FFCCBB">
    <td  onClick="Expand('TRGroupCode_2','TDGroupCode_2')" id="TDGroupCode_2">+</td>
    <td>2_1</td>
    <td>2_3</td>
  </tr>
  <tr id="TRGroupCode_2_1" style="display:none" bgcolor="#CCCCCC">
    <td>2_1</td>
    <td>2_1</td>
    <td>2_1</td>
  </tr>
  <tr id="TRGroupCode_2_2" style="display:none" bgcolor="#CCCCCC">
    <td>2_2</td>
    <td>2_2</td>
    <td>2_2</td>
  </tr>
  <tr id="TRGroupCode_2_3" style="display:none" bgcolor="#CCCCCC">
    <td>2_3</td>
    <td>2_3</td>
    <td>2_3</td>
  </tr>
  <tr id="TRGroupCode_3" bgcolor="#FFCCBB">
    <td  onClick="Expand('TRGroupCode_3','TDGroupCode_3')" id="TDGroupCode_3">+</td>
    <td>3_1</td>
    <td>3_4</td>
  </tr>
  <tr id="TRGroupCode_3_1" style="display:none" bgcolor="#CCCCCC">
    <td>3_1</td>
    <td>3_1</td>
    <td>3_1</td>
  </tr>
  <tr id="TRGroupCode_3_2" style="display:none" bgcolor="#CCCCCC">
    <td>3_2</td>
    <td>3_2</td>
    <td>3_2</td>
  </tr>
  <tr id="TRGroupCode_3_3" style="display:none" bgcolor="#CCCCCC">
    <td>3_3</td>
    <td>3_3</td>
    <td>3_3</td>
  </tr>
  <tr id="TRGroupCode_3_4" style="display:none" bgcolor="#CCCCCC">
    <td>3_4</td>
    <td>3_4</td>
    <td>3_4</td>
  </tr>
  </table>
</body>
</html>