Pls Help Me

[admin]

The code about adding or removing items between two select objects:

....
<SCRIPT language="JavaScript">

function submitAdd(){
var i,j, selectNum,remListNum;
var optionele,eleText,eleValue;
selectNum = document.UserSelectedForm.unassignedUsers.options.length;
remListNum = document.UserSelectedForm.assignedUsers.options.length;

document.UserSelectedForm.unassignedUsers.focus();

if( document.UserSelectedForm.unassignedUsers.selectedIndex == -1)
{
alert("Please select a user to add.");
return false;
}
else{
j = remListNum;
document.write("You've selected the following options:\n")
for( i=0; i < selectNum; i++)
{
if(document.UserSelectedForm.unassignedUsers.options.selected)
{
// get the text and value of the selected item
eleText = document.UserSelectedForm.unassignedUsers.options.text;
eleValue = document.UserSelectedForm.unassignedUsers.options.value;

// remove this option from the unassignedUserList
deleteAnItem(document.UserSelectedForm.unassignedUsers,i);

// chanage the focus
document.UserSelectedForm.unassignedUsers.blur();
document.UserSelectedForm.assignedUsers.focus();

// construct the option
optionele = new Option(eleText,eleValue);

// add the item to the assignedUserList
eval("inForm.assignedUsers.options[j]=optionele");

j++;

// restore the focus
document.UserSelectedForm.assignedUsers.blur();
document.UserSelectedForm.unassignedUsers.focus();
}
}
return true;
}
}


function submitRemove(){
var i,j, selectNum,addListNum;
var optionitem,itemText,itemValue;
selectNum = document.UserSelectedForm.assignedUsers.options.length;
addListNum = document.UserSelectedForm.unassignedUsers.options.length;

if( document.UserSelectedForm.assignedUsers.selectedIndex == -1)
{
alert("Please select a user to remove.");
return false;
}
else{
j = addListNum;

document.write("You've selected the following options:\n")
for( i = 0;i < selectNum ;i++ )
{
if(window.document.UserSelectedForm.assignedUsers.options.selected)
{
// get the text and value of the selected item
itemText = window.document.UserSelectedForm.assignedUsers.options.text;
itemValue = window.document.UserSelectedForm.assignedUsers.options.value;

// remove this option from the unassignedUserList
deleteAnItem(window.document.UserSelectedForm.assignedUsers,i);

// chanage the focus
window.document.UserSelectedForm.assignedUsers.blur();
window.document.UserSelectedForm.unassignedUsers.focus();

// construct the option
optionitem = new Option(itemText,itemValue);

// add the item to the assignedUserList
eval("window.document.UserSelectedForm.unassignedUsers.options[j]=optionitem");

j++;

// restore the focus
window.document.UserSelectedForm.unassignedUsers.blur();
window.document.UserSelectedForm.assignedUsers.focus();
}
}
return true;
}
}

function submitBack(){
var i = 0,remListNum;

remListNum = document.UserSelectedForm.unassignedUsers.options.length;

// focus on the assignedUserList
document.UserSelectedForm.assignedUsersList.focus();

while( i < remListNum )
{

if(!(document.UserSelectedForm.assignedUsers.options.selected))
{
document.UserSelectedForm.assignedUsers.options.selected = true;
}
}
}

</SCRIPT>


<FORM name="UserSelectedForm" onsubmit="return submitBack()" method="post">

<P><B><FONT size="4">Manage Users</B></P>
<TABLE cellSpacing=2 cellPadding=2 width=500 border=0>
<TBODY>
<TR>
<TD colSpan=2>
<TABLE borderColor=#cccccc cellSpacing=0 cellPadding=0 width="100%"
border=1>
<TBODY>
<TR>
<TD><B>Search for users</B><BR>
<TABLE>
<TBODY>
<TR>
<TD>&nbsp;Search by user name:<BR></TD>
<TD><INPUT type="text" name="keyword" value=http://www.webdeveloper.com/forum/archive/index.php/""> </TD>
<TD><INPUT class=primarybutton type=submit value=" Go "
name="go"><BR><BR></TD>
</TR>
<TR>
<TD colSpan=3>
<DIV align=center><A
href="<%= showAllUsersURI %>">Show all available Users</A></DIV>
</TD>
</TR>
</TBODY>
</TABLE>
</TD>
</TR>
</TBODY>
</TABLE>
</TD>
</TR>

<TR>
<TD colSpan=2></TD>
</TR>


<TR>
<TD>&nbsp;&nbsp;4 Users are listed<BR><SELECT
style="WIDTH: 218px; HEIGHT: 246px" multiple size=15
name="unassignedUsers">
<OPTION value="Z"> z</OPTION>
<OPTION value="h"> h </OPTION>
<OPTION value="w"> w </OPTION>
<OPTION value="e"> e </OPTION>
<OPTION value="i"> i </OPTION>
<OPTION value="u"> u </OPTION>
</SELECT>
</TD>

<TD align=left>&nbsp;&nbsp;0 users have been attached<BR><SELECT
style="WIDTH: 218px; HEIGHT: 246px" multiple size=15
name="assignedUsers">
<OPTION value = "doudou">doudou </OPTION>
</SELECT>
</TD>

</TR>

<TR>
<TD align=middle><BR><INPUT type="button" onclick = " return submitAdd()" value=" Add " name="addBtn">
</TD>
<TD align=middle><BR><INPUT type="button" onclick = "return submitRemove()" value=" Remove " name="remBtn">
</TD>
</TR>

<TR>
<TD align=middle colSpan=2><BR><BR><INPUT type=submit onsubmit="submitBack()" value=" Back to Software Edit Page " name="backBtn"></TD>
</TR>
</TBODY>
</TABLE>
</FORM>

..........

when I click on the "Add" button, an error appears, remind me the "document.UserSelectedForm.unassignedUsers" is null or not an object. I don't know why. I can use the name of the Select object directly,right? In the case adding or removing multiple items between two selection, which way is better? Thanks MILLION!