Validate CheckboxList Control with javascript to make sure atleast one checkbox is checked

While developing one page which sends mail to the selected group from the checkbox list I got requirement to impose validation to check atleast one group should be selected.

Here is the solution.....

< id="CvalGroupCheckbox" display="Dynamic" runat="server" cssclass="MsgLabel" errormessage="" clientvalidationfunction="validateGroupSelection">

< language="javascript" type="text/javascript">

function validateGroupSelection(source, arguments) {
document.getElementById("").style.visibility = "hidden";
var chkSubUsers = document.getElementById('_0');
var chkTestUsers = document.getElementById('_1');

if ((!chkSubUsers.checked) && (!chkTestUsers.checked))
arguments.IsValid = false;
else
arguments.IsValid = true;
}

< /script>

Happy programming.... :)