Response to: How To Show alert message when file already exists(When Browsing for a new file) in asp.net

Revision 2
File exists: System.IO.File.Exists.

Showing: many methods are available; I would recommend this:

<p><% some_C#_expression_calculating_the_message_text %></p>

Note that the by existing file you can only mean some file in the file system of the host where the HTTP server works. Consequently, you can only calculate existence on the server part, which makes the "showing" easy: the content is returned in the HTTP response anyway.

—SA