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For Beginners: In ASP.NET how to show a Javascript Alert message box?

Posted by Paul on December 2, 2010

I have seen frequently that beginners in ASP.NET try to use Windows Forms MessageBox and fails.

I would like to say that MessageBox class is meant for Windows Forms Application and not ASP.NET Web applications.

In ASP.NET applications, you have to:

Use either a page to show the message


Use javascript alert function to show the message (the example is given below)


Create a new web application using File > New Project > Web > ASP.NET Web Application


In the solution Explorer, right click on the Default.aspx and use View Code command.

Replace the Page_Load method code as below:

protected void Page_Load(object sender, EventArgs e)


    string message = "Test Message Box in ASP.NET";

    string script = "<script language=’javascript’>alert(‘" + message + "’);</script>";

    ClientScript.RegisterStartupScript(GetType(), "key", script);


Now you can execute the application.


On loading the page you will see the following message box (if not enable javascript in your browser)



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