How to use CustomValidator with dropdown list

Here is an example of using CustomValidator with  dropdown list in asp.net application

Step 1 : Write  java script function
< script type="text/javascript" language="javascript" >

function CheckWorker(sender, args) {
                var worker = $get('<%=ddlstWorkers.ClientID %>');
                if (worker.selectedIndex == 0) {
                    args.IsValid = false;
                    return;
                }
                args.IsValid = true;
            }

< / script>

Step 2: Define the asp:DropDownList and CustomValidator

< asp:DropDownList ID="ddlstWorkers" runat="server" CssClass="ddl" Style="width: 220px;">

                                        < /asp:DropDownList >

                                        < asp:CustomValidator ID="cvWorker" runat="server" ControlToValidate="ddlstWorkers"   Display="None" ErrorMessage="Select a worker." ClientValidationFunction="CheckWorker" >< /asp:CustomValidator >