I was going to spend this evening working on #webactions browser extension, but I think it would be better spent providing a #backup/data export utility for fellow ex #diaspora users.
From my initial researches, it looks like
/u/username.json is the best bet, as it gives a JSON array of all posts written by
username, along with like and comment data. It accepts a
max_time=timestamp query param, and a
_ query param, the function of which I am not sure of.
To iterate through all the pages of posts from a certain user, start with their profile URL w/
.json tacked on the end, fetch all the items, get the datetime of the last item, convert that to a timestamp, fetch the same URL with
?max_time=timestamp, repeat until an empty array is returned.