Display exception message using JavaScript in Base Page's OnError event - asp.net

Question

I want to display all unhandled excpetions in the appplication using Javascript. For this I have defined onError event inside my custom base class of my pages. Here is the code for my Base Page:
namespace Loan
{
public class BasePage : System.Web.UI.Page
{
public BasePage()
{
}
protected override void OnError(EventArgs e)
{
//Report Error
Exception ex = Server.GetLastError();
if (ex is HttpUnhandledException && ex.InnerException != null)
{
ex = ex.InnerException;
}
var _message = "Error : "+ ex.Message.ToString();
DisplayAlert(_message);
Server.ClearError();
return;
}
protected virtual void DisplayAlert(string message)
{
ClientScript.RegisterStartupScript(
this.GetType(),
Guid.NewGuid().ToString(),
string.Format("alert('{0}');", message.Replace("'", #"\'")),
true
);
}
}
}
The alert is never displayed for an unhandled exception. However, if I call the DisplayAlert from any Page
base.DisplayAlert(ex.Message);
the javascript alert is displayed. How can I get the javascript alert to be displayed for the unhandled exceptions from the base page.Or is there any other way to display these exception messages to the user. I don't want to redirect them to a generic error page as it sends them back and forth.

Answer 1

This is expected. If the exception is unhandled, the OnError event on BasePage will execute and your child page won't continue to execute, there's nothing to render as the BasePage is pure code. If you want to spit out the alert you'd need to write directly to the Response but you should still see a blank page after an unhandled exception occurs.
protected virtual void DisplayAlert(string message)
{
Response.Write(string.Format("<script>alert('{0}');</script>", message.Replace("'", #"\'")));
}
Of course, when you call DisplayAlert directly, it works because you are just calling a method, the Page execution continues normally.
I frankly dislike your approach. You should log the exception and redirect to another page, the typical Oooooooooopsss, me screwed up kind of thing.