@siam009 Forgive my careless response - Pablo’s answer is correct! My recommendation above won’t work because of the limitations of UXP right now. To add to his answer, you’ll find that getFileForOpening() and getFileForSaving() both require user interaction via a file picker dialog.
I would refer to this post: Read currently opened images - #2 by amandah and use a similar workflow (create/save csv file in the plugin folder or the data folder).