Many user scripts and gadgets, such as Twinkle, UserMessages, etc., need
to post on various talk pages.
With the development of Flow, there are now two possible types of talk
pages to deal with (not counting LQT, which this solution does not
handle), old-style and Flow. User talk pages are already starting to
use Flow on a very limited opt-in basis (I think the number is still
less than I have fingers).
Now, you can use MessagePoster to post to a page without knowing this
information ahead of time. The documentation is at
https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/mw.messagePoster.…
, and you can see an example of how it's used at
https://git.wikimedia.org/blob/mediawiki%2Fcore.git/977f7ad8ade23a7ce5326a9…
.
Feel free to reply, or ask on #wikimedia-collaboration, if you have any
questions.
Matt Flaschen