validation more than zero

 function fnChkNumVal(source, args) {
            //var iknum = parseInt(args.Value)
            var iknum =args.Value
            if(iknum==0)
                 args.IsValid = false;
            else
                 args.IsValid = true ; 
        }

 <asp:TextBox ID="txtNWOnlineTransAmt" MaxLength="16" runat="server" CssClass="input">

  <asp:CustomValidator ID="CustomValidator19" runat="server" ErrorMessage="Transaction amount can not be zero"
                                                    EnableClientScript="true" SetFocusOnError="true" ClientValidationFunction="fnChkNumVal"
                                                    ControlToValidate="txtNWOnlineTransAmt" ValidationGroup="Feedback" Display="None"
                                                    CssClass="commment"></asp:CustomValidator>