Show "passed" image or text after validating an asp.net (req. field)validator

I have the following asp.net code:

<asp:TextBox CssClass="mf" runat="server" ID="mail1" Width="270" />
<asp:RequiredFieldValidator ID="rfv1" 
                            runat="server" 
                            ControlToValidate="mail1" 
开发者_StackOverflow社区                            Display="Dynamic" />

Now I want to show an image (or text) if the validation passes on the fly (no postback)

A jQuery solution is also fine by me, but that wouldn't be so safe if javascript is disabled.

Without relying on an external framework you can tap into the ASP.Net Client Side Validation framework to handle extended/advanced functionality. In this way you are working with the framework, augmenting it instead of replacing it.

A tiny bit of JavaScript is all that is needed to enable the behavior you want.

<asp:TextBox CssClass="mf" runat="server" ID="mail1" Width="270" OnChange="showValidationImage();" />
<asp:RequiredFieldValidator ID="rfv1" 
                        runat="server" 
                        ControlToValidate="mail1" ClientIDMode="Static"
                        Display="Dynamic" >
    <img src="../Image/fail.jpg" />
</asp:RequiredFieldValidator>
<img id="imgPass" src="../Image/pass.jpg" style="visibility:hidden" />
<script language="javascript">
    // This function will be called whenever the textbox changes
    // and effectively hide or show the image based on the state of
    // the client side validation.
    function showValidationImage() {
        if (typeof (Page_Validators) == "undefined") return;

        // isvalid is a property that is part of the ASP.Net
        // client side validation framework
        imgPass.style.visibility = rfv1.isvalid ? "visible" : "hidden";
    }
</script>
<br />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" />

Notice here that I am using a feature of ASP.Net 4 with ClientIDMode="Static" if you are not using .Net 4 then you will need to use the standard <%= rfv1.ClientID %> server side include to get at the client id inside your script.