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CustomValidator.ClientValidationFunction Property

Gets or sets the name of the custom client-side script function used for validation.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

public string ClientValidationFunction { get; set; }
<asp:CustomValidator ClientValidationFunction="String" />

Property Value

Type: System.String
The name of the custom client script function used for validation. The default value is String.Empty, which indicates that this property is not set.

The function name should not include any parentheses or parameters.

Set this property to the name of the function that performs the client-side validation.

Because the client validation function runs on the target browser, the function must be written using a scripting language supported by the browser, such as JScript or VBScript.

This property cannot be set by themes or style sheet themes. For more information, see ThemeableAttribute and ASP.NET Themes and Skins Overview.

Walkthrough: Validating User Input in a Web Forms PageBuilding ASP .NET Web Applications in Visual Studio

The following code example demonstrates how to use the ClientValidationFunction property to specify the name of the function that performs client-side validation. The validation function checks for even numbers. For a description of the function parameters, see the Remarks section of the CustomValidator class overview.

Security noteSecurity Note:

This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

<%@ Page Language="C#" AutoEventWireup="True" %>


   <script runat="server">

      void ValidateBtn_OnClick(object sender, EventArgs e) 
         // Display whether the page passed validation. 
         if (Page.IsValid) 
            Message.Text = "Page is valid.";

            Message.Text = "Page is not valid!";

      void ServerValidation(object source, ServerValidateEventArgs args)
            // Test whether the value entered into the text box is even. 
            int i = int.Parse(args.Value);
            args.IsValid = ((i%2) == 0);

         catch(Exception ex)
            args.IsValid = false;



   <form id="Form1" runat="server">

      <h3>CustomValidator ServerValidate Example</h3>

      <asp:Label id="Message"  
           Text="Enter an even number:" 


      <asp:TextBox id="Text1" 
           runat="server" />


      <asp:CustomValidator id="CustomValidator1"
           ErrorMessage="Not an even number!"


      <asp:Button id="Button1"


<script language="javascript"> 
   function ClientValidate(source, arguments)
        if (arguments.Value % 2 == 0 ){
            arguments.IsValid = true;
        } else {
            arguments.IsValid = false;

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0