Hello all,
In order to allow better gadget integration, JavaScript hooks documented in the hooks-js.txt https://phabricator.wikimedia.org/diffusion/EWBA/browse/master/docs/hooks-js.txt file delivered together with Wikibase source code are considered stable. We just added this information in the stable interface policy https://www.wikidata.org/w/index.php?title=Wikidata%3AStable_Interface_Policy&type=revision&diff=741948123&oldid=716051185.
If you have any question about this, feel free to ping me. Cheers,