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JavaScript Detection in ASP.NET

Chona1171

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12 Apr 2009

Explains how to detect if clients have the JavaScript feature turned on.

Introduction

I have been trying the whole of last week to figure out a way to detect if the client has JavaScript activated on his browser.

Background

I have found a rather useful method for the server side: Request.Browser.JavaScript. This returns a boolean value indicating if the browser is capable of running JavaScript. The problem, however, is that the browser might be capable of running scripts, but it does not mean the user has turned it on yet.

I have tried many techniques, running the JavaScript in the header, changing the property of an HtmlItem, etc., but couldn't get a true/false indicator on the server side, mainly because the server side executes before any JavaScript can change properties. And finally, last night, I thought of another way of doing it:

The Code

Everything is done in the code-behind page, and makes use of cleverly placed Session variables.

protected void Page_Load(object sender, EventArgs e)
{
    //JSChecked -indicates if it tried to run the javascript version
    //JS Works - Inicates whether javascript works or not
 
    if (Session["JSChecked"] == null)
    {
        Session["JSChecked"] = "Checked";
        Response.Write(@"<script language="'javascript'" type" + 
                       @"='text/jscript'>   window.location  " + 
                       @"= 'default.aspx?JScript=1'; </script>");
    }
    //If the javascript Above executed JScript will have a value 
    if (Request.QueryString["JScript"] != null)
    {
        Session["JsWorks"] = "True";
    }
    
    if (Session["JsWorks"] == null)
    // Work under initial assumption that Javascript Doesnt Work
    // On first load
    {
        Session["JsWorks"] = "False";
        //Does Javascript Work
    }
 
    if (Session["JsWorks"].ToString().Equals("False"))
    // Work if JS Is Set to False
    {
        //Load Non Javascript Content
    }
    else
    {
        //Load Javascript enabled content
    }
}

This is a technique to run JavaScript using the code-behind. This will execute at the very top before the <html> tags are loaded.

Response.Write(@"<script language="'javascript'" type='text/jscript'>" + 
               @" window.location = 'default.aspx?JScript=1'; </script>");

Points of Interest

The technique to run JavaScript in the code-behind can also be a very easy way of debugging your application if you use alert(''); methods within the script tag.

Please view my new article on how to achieve this using the Script Manager and a PageMethod call:

http://www.codeproject.com/KB/aspnet/JavaDetectService.aspx

History

Last update - 19/04/2007.

License

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