Plugins

Offical Documentation: https://docs.joomla.org/Plugin

Plugins are the event driven code in Joomla. Components raise events and plugins that have registered observers for those events will run in the order set in the admin plugin manager.

Note that the jeventdispatcher class used in j3 is deprecated and to be replaced with a new event class in j4.

Other Resources

Video: https://www.youtube.com/watch?v=dNTeqkc0g4A

Book: https://www.yireo.com/books/programming-joomla-plugins-book