Checkboxlist validation using Custom Validator in ASP.NET

Aspx Code

<asp:CheckBoxList ID="CheckBoxListStates" runat="server" ClientIDMode="Static">
<asp:ListItem Text="Preliminary Construction" Value="prelim_construction" />
<asp:ListItem Text="Final Construction" Value="final_construction" />
<asp:ListItem Text="Construction Alteration" Value="construction_alteration" />
<asp:ListItem Text="Remodel" Value="remodel" />
</asp:CheckBoxList>

<asp:CustomValidator runat="server" ID="cvmodulelist" ClientValidationFunction="ValidateModuleList" Display="Dynamic" ErrorMessage="Please select state">
</asp:CustomValidator>

JavaScript Code

function ValidateModuleList(source, args) {

var chkListModules = document.getElementById('<%= CheckBoxListStates.ClientID %>');

var chkListinputs = chkListModules.getElementsByTagName("input");

for (var i = 0; i < chkListinputs.length; i++) {

if (chkListinputs[i].checked) {

args.IsValid = true;

return;

}
}
args.IsValid = false;
}