From Joomla! Documentation
This page contains an index to the set of Joomla API Guides. These guides aim to help you understand how to use these Joomla functions in your own Joomla extensions.
Each API guide includes sample code which you can copy and install in your own development environment. Generally these code samples are written to be included and installed as Joomla module, so if you're not familiar with Joomla module development you may find going through the short series Creating a Simple Module useful.
Note that this is work in progress!
Around Joomla 3.8 the Joomla development team began changing the naming convention of Joomla classes to use namespaces, so that for example JFactory changed to Factory in the Joomla\CMS namespace. As you read existing Joomla code and documentation you may find the classes following either the new or the old naming standard. You can find the mapping between the two naming conventions in the libraries/classmap.php file in your Joomla instance.
- Categories Using the Categories and CategoryNode classes to access data relating to Joomla categories
- Database / JDatabase. There are two API guides, covering Selecting data using JDatabase and Inserting, Updating and Removing data using JDatabase
- Form / JForm. There is a Basic guide to using the Joomla Form API and incorporating forms within a Joomla component.
- Input / JInput Using the Input class to obtain the values of parameters in HTTP GET and POST requests
- Log / JLog Log messages (eg error messages, debug messages) to a log file, and optionally to the debug console
- Menu and Menuitems
- Table / JTable provides functionality for performing CRUD operations (and more) on database tables. The guide is split into a Basic API Guide and an Advanced API Guide
- User / JUser API related to the Joomla User.