CheckBoxList Required Validation in Javascript

ASP.NET CODE:

<asp:CheckBoxList ID="chkList" runat="server">
            <asp:ListItem>Item One</asp:ListItem>
            <asp:ListItem>Item two</asp:ListItem>
            <asp:ListItem>Item three</asp:ListItem>
            <asp:ListItem>Item four</asp:ListItem>
        </asp:CheckBoxList>
        <asp:Button ID="btnSubmit" runat="server" ValidationGroup="CHK" OnClientClick="return validateChk();" Text="Validate"/>

JAVASCRIPT CODE:

function validateChk() {
            debugger;
            var found = false;
            var validated = false;
            var id = document.getElementById("<%=chkList.ClientID %>").id;
            var elements = document.forms[0].elements;
            for (i = 0; i < elements.length; i++) {
                if (elements[i].type == "checkbox" && elements[i].id.indexOf(id) > -1) {
                    found = true;
                    if (elements[i].checked) {
                        validated = true;
                        break;
                    }
                }
            }
            if (found && validated)
                return true;
            else
                return false;
            
        }