Validate ASP.Net CheckBoxList control using JavaScript.

<asp:CheckBoxList ID="CheckBoxList1" runat="server">
    <asp:ListItem Text = "One" Value = "1"></asp:ListItem>
    <asp:ListItem Text = "Two" Value = "2"></asp:ListItem>
    <asp:ListItem Text = "Three" Value = "3"></asp:ListItem>
</asp:CheckBoxList>

<script type = "text/javascript">
var atLeast = 1

function Validate()
{
   var CHK = document.getElementById("<%=CheckBoxList1.ClientID%>");
   var checkbox = CHK.getElementsByTagName("input");
   var counter=0;

   for (var i=0;i<checkbox.length;i++)
   {
       if (checkbox[i].checked)
       {
            counter++;
       }
   }

   if(atLeast>counter)
   {
        alert("Please select atleast " + atLeast +  " item(s)");

        return false;
   }
   return true;
}
</script>