If I have form where user can upload files via Ajax (and upload is available only when JavaScript is turned on) and some other text fields etc. What if is user opens a new page for same form. Should that show already uploaded files, or are uploaded files only related to page where files where uploaded? I am asking this because I don't know what is common convention in these kind of situations.
I don't know that there is any convention, but if you have an authenticated user and you know that the user has uploaded a file for a certain form, I think it's a good idea to present the already uploaded file on the second instance of the form.
Key benefits are time, space and bandwidth saved by discouraging duplicate uploads. Another benefit is the perception that you are helping the user accomplish their task by eliminating the need to re-upload a file.
And I can't think of any drawbacks to showing the already uploaded files.
Hope this helps!