Tips & Tricks for ASP.NET - C#

<script language="javascript">

function abc(sender, args) {   

//false condition{
args.IsValid = false;   
//}
}

</script>

        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:CustomValidator ID="CustomValidator1" runat="server"
            EnableClientScript="true" Display="Dynamic"
            ClientValidationFunction="abc" ControlToValidate="TextBox1"
            ErrorMessage="CustomValidator"

ValidateEmptyText="True"></asp:CustomValidator>