Cleaning up automatically when leaving a page

Hi all, I have a php application for which I have a page which creates temporary junk and puts it into a persistent store (in this case a postgres database, but that is beside the point.) I have a Save button which puts the stuff I really want into the persistent store and cleans up the temporary junk. I have a Cancel button which only cleans up the temporary junk. I would really like to have the cleanup code run anytime a user leaves the page without hitting the Save button. Is there anyway to do this? I.e. have php code called conditionally on exiting the page? Thanks Mary