Always wanted to test if the client's browser has javascript disabled in their browser ? Sounding impossible ? Well, not anymore! 

Ok, so as Web2.0 applications are increasing in popularity and we are all starting to enable a lot of clientside javascript in our web applications, especially the use of ajax extentions and the updatepanel, we also know how this is all going to break for users who have javascript turned off or whose browsers do not support javascript.

Now, lets be real, it's not very common nowadays for a useragent to not support javascript, all the big players support it well(IE, Firefox, Opera, Safari).

However what about users that have javascript turned off ? Personally, I don't want my applications breaking on potential clients who fall in this category and realistically, today, there is no way to test for sure if the client turned off javascript. Sure, I am aware of the HttpBrowserCapabilities class, specifically the EcmaScriptVersion property. However this is a pretty useless property to me in this usage scenario since it only tells me what version of javascript the users client browser supports. This is simple static information passed on by the clientbrowser when making the request.

What we need is to know "Is javascript turned off ?" Knowing this is important in today's applications because it allows us to gracefully exit, or provide a serverside alternative, a non script version of our page being requested.

As of this writing I have not found any clear answer anywhere, so i have invested a couple of minutes to come up with the following solution. It's quite simple and should be working 100% without breaking, telling us exactly what we are seeking. -->> Hey, you there making the request, do you have javascript enabled/disabled ?

The idea is to introduce a piece of js code when the first request is being made by the client. Particularly a piece of code that can tell us serverside, "yes, javascript is enabled", without any delay or rendering much content to the client.

<script type="text/javascript">
window.location.href='http://weblogs.asp.net/Default.aspx?supportsjs=true';
</script>

if javascript is enabled, the clients page will redirect, but what if js is disabled ? this script wont do anything, so to address this, we will introduce a second piece of code as well :

<meta http-equiv="refresh" 
content="0;url=http://weblogs.asp.net/Default.aspx?supportsjs=false" />

That's it. If js is disabled, this second line will kick off and postback. Perfect.

Still, we don't want to do this everytime. We want to do this for the first request only, so what we can do is set a serverside flag in session state. I don't really recommend using session state because I find sessions to be unreliable, but that's just me. You basically have no control on when the session recycles. My preference lies in the profile provider(which is going to persist the value in the database and in style), however for simplicity, i'm setting a flag in session state.

Update october 4th,2007 : Initially, as you have read above in this post, i was planning on using the meta refresh tag if js was indeed disabled on the client. It was also a useless effort, when I couldof just assumed js was disabled from the start and only enabled if the js script fired the postback. As you will note from Richards comment below, the meta refresh tag only brings other problems to the table as it can in turn be disabled invidividually by the browser and not only in IE or Firefox but opera has support for this too. Here is the updated code that checks for javascript without meta refresh tag getting in the way.

Following is the code :

<%@ Page Language="C#" %>
<script runat="server">
    /*
     do it in init, otherwise you cannot 
     set ScriptManager.EnablePartialRendering property
     */
    protected void Page_Init(object sender, EventArgs e)
    {
        bool notSet = string.IsNullOrEmpty(this.Request.QueryString["supportsjs"]);
        string url = this.Request.Url.OriginalString;
        if (notSet && Session["supportsjs"] == null)
        {
            string queryStringKey = (this.Request.QueryString.Count > 0) ?
                "&amp;supportsjs=" : "?supportsjs=";
            string jsTesterScript = string.Format(
           "<{0} type=\"text/javascript\">window.location.href='{1}{2}true'</{0}>",
           "script", url, queryStringKey);
            Response.Write(jsTesterScript);
            Response.Flush();
        }
        if (Session["supportsjs"] == null)
            Session["supportsjs"] = false;// default, assume false
       // if our js code posted back, 
       // and we still hold default assumption,
       // then client does indeed support js
       // so update the session
       if (!notSet && !(bool)Session["supportsjs"])
           Session["supportsjs"] = true;    
       ScriptManager1.EnablePartialRendering = (bool)Session["supportsjs"];
    }
</script>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" 
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
        <h1>outside updatepanel : <%= DateTime.Now %></h1>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
           <ContentTemplate>
                <h1>Inside updatepanel : <%= DateTime.Now %></h1>
               <asp:Button ID="Button1" runat="server" Text="Button" />
           </ContentTemplate>
        </asp:UpdatePanel>
        <div>
        </div>
    </form>
</body>
</html>