Change error page by file type?

[Rt Ibmer]

Hello,

If someone makes a request for a .js file from our server and no such file exists, I would like to return a different error page (actually an error.js page) in response.  Yet if they request a .htm page I want to use a different error page (notfound.htm).  Is this possible? If so can you please show an example configuration file snippet to do this? Thank you!