Single checkbox not selected

Question

I know this is not a javscript forum.. (WISH THERE WAS ONE On SUN.COM)..and i am sorry to post it here.. but the problem is JSP and javascript
I have multiple checboxes.. Something like Yahoo mail.. When the inbox is opened the number of checkboxes correspond to the number of mails on that page..along with an extra one at the very top(called it Header_checkbox).. If header_checkbox is selected.. all the mails are selected and one can either delete or move the mails..
My form is kinda similar.. I have multiple rows.. and depending on the number of rows, the checkboxes are displayed.. the Javascript function works fine if there are more than one checkboxes...It doesnt work if theres a single one.. well not a big deal since the user can click on the single checkbox and it shld be fine.. but i am curious to know why it isnt working for a single one. When i try to display the checkbox.length it gives me "undefined" (this is incase theres only one chekcbox)... for multiple chekcboxes it gives the rite number.
Heres the code if anyone has suggestions
Thank you
function toggle(frm)
   var checkbox_length = frm.checks.length;
    alert(checkbox_length);
   for( var i = 0; i < checkbox_length; i++ )
      frm.checks.checked = frm.tog.checked;
[HTML CODE]
<FORM name="editFormatForm" method="post" action="edit_delete_filetype_format.jsp">
<tr class="titleitem">
<td><input type="checkbox" name="tog" onclick="javascript:toggle(this.form);"></td>
<td>Fieldname��</td>
<td>Format��</td>
<td>Unique?</td>
<td>Optional?</td>
<td>Description</td>
<td></td><td></td>
</tr>
<%
if (fileTypeList.size() > 0)
for (int k = 0; k < fileTypeList.size(); k++)
formatObject = (FiletypeFormatObject) fileTypeList.get(k);
id = formatObject.getId();
columnName = formatObject.getColumnName();
columnFormat = formatObject.getColumnFormat();
uniqueness = formatObject.getColumnUnique();
description = formatObject.getDescription();
optional_int = formatObject.getColumnOptional();
count++;
%>
<tr class="<%=htmlObj.getClassString(count)%>">
<td><input type="checkbox" name="checks" value="<%=id%>"></td>
<td><input type="text" name="columnName" value="<%=columnName%>"></td>
<td><input type="text" name="columnFormat" size='30' value="<%=columnFormat%>"></td>
<td><input type="checkbox" name="unique" <% if(uniqueness == 1) { %> checked <%}%>></td>
<td><input type="checkbox" name="optional" <% if (optional_int == 1) { %> checked <%} %>></td>
<td><input type="text" name="description" value="<%=description%>"></td>
</tr>
<% } } count++; %>
<tr class="<%=htmlObj.getClassString(count)%>"><td></td><td><input type="submit" value="Submit Changes"></td>
<td colspan="12"><input type="submit" value="delete"></td></tr>
<% count++; %>
<tr class="<%=htmlObj.getClassString(count)%>"><td></td><td colspan="12">�</td></tr>
<% count++; %>
<tr class="<%=htmlObj.getClassString(count)%>"><td></td><td><input value="Enter New Field..."></td>
<td><input value=""></td><td><input type="checkbox"></td><td><input type="checkbox"></td>
<td><input type="submit" value="Add Field"></td><td></td></tr>
</FORM>
[END OF HTML CODE]

Answer 1

The browser creates a DOM (Document Object Model) of the document and the elements in the document. In this DOM it references the elements on the page by name. If there is more than one element with the same name it creates an array of these elements and puts the array in the DOM but if there is only one element it places this element in the array.
If there is only one checkbox with the name "checks" this will be the object referred to as "rm.checks" and this element doesn't have an length property.
function toggle(frm)
var checkbox_length = frm.checks.length;
if (checkbox_length != undefined) {
    for( var i = 0; i < checkbox_length; i++ )
       frm.checks.checked = frm.tog.checked;
} else {
frm.checks.checked = frm.tog.checked;