You can use Ajax to request their user page, and in the json it should specify all of the groups they're in.
ah sorry forgot to reply here,
meantime I found out, that its not a problem in custom JS to use app.user.groupTitle 🙂
it works fine so good
i want to write code to custom import (from old phpbb system, but with custom requirements).
I wrote at first a nice code that work via the API (write plugin, with global key)
But I understand that this is not the right way for import job:
I understand that I have to work directly with the database, but I'm afraid I will not do it properly - I did not find a documentation of what to do with adding a topic, or a replay. I also feel a danger of ingorn all the validation and logic of nodebb system.
I'd love to know how you do
Your best shot is probably to fork off https://github.com/psychobunny/nodebb-plugin-import-phpbb and use nodebb-plugin-import with your custom modifications.