Apply validation radio button list using JavaScript in asp.net

Apply validation radio button list using JavaScript in asp.net

  function ValidateRadioButtonList(source, arguments) {
        var RBL = document.getElementById(source.controltovalidate);
        var radiobuttonlist = RBL.getElementsByTagName("input");
        var counter = 0;
        var atLeast = 1
        for (var i = 0; i < radiobuttonlist.length; i++) {
            if (radiobuttonlist[i].checked) {
                counter++;
            }
        }
        if (atLeast = counter) {
            arguments.IsValid = true;
            return arguments.IsValid;
        }
        arguments.IsValid = false;
        return arguments.IsValid;
    }

    <asp:RadioButtonList ID="rblCOBC" runat="server" RepeatDirection="Horizontal">
       <asp:ListItem Text="Yes" Value="1"></asp:ListItem>
       <asp:ListItem Text="No" Value="0"></asp:ListItem>
    </asp:RadioButtonList>

    <asp:CustomValidator runat="server" Display="Dynamic" ValidateEmptyText="true" ClientValidationFunction="ValidateRadioButtonList"
                                ID="CtmrblCOBC" ValidationGroup="gpAddUser" ControlToValidate="rblCOBC" ErrorMessage="Required"></asp:CustomValidator>