ext_localconf.php

Should not be used for

While you can put functions and classes into ext_localconf.php, it considered bad practice because such classes and functions would always be loaded. Move such functionality to services or utility classes instead.

Registering hooks, XCLASSes or any simple array assignments to $GLOBALS['TYPO3_CONF_VARS'] options will not work for the following:

• class loader
• package manager
• cache manager
• configuration manager
• log manager (= Logging Framework)
• time zone
• memory limit
• locales
• stream wrapper
• error handler
• Icon registration. Icons should be registered in Icons.php.

This would not work because the extension files ext_localconf.php are included (loadTypo3LoadedExtAndExtLocalconf) after the creation of the mentioned objects in the Bootstrap class.

In most cases, these assignments should be placed in config/system/additional.php.

Example:

Register an exception handler:

$GLOBALS['TYPO3_CONF_VARS']['SYS']['debugExceptionHandler'] =
    \Vendor\Ext\Error\PostExceptionsOnTwitter::class;

Should be used for

These are the typical functions that extension authors should place within file:ext_localconf.php

• Registering hooks, XCLASSes or any simple array assignments to $GLOBALS['TYPO3_CONF_VARS'] options
• Registering additional Request Handlers within the Bootstrap
• Adding any page TSconfig
• Adding any user TSconfig
• Adding default TypoScript via \TYPO3\CMS\Core\Utility\ExtensionManagementUtility APIs
• Registering Scheduler Tasks
• Adding reports to the reports module
• Registering Services via the Service API

<?php

declare(strict_types=1);

use MyVendor\MyExtension\MyClass;

defined('TYPO3') or die();

// Add your code here
MyClass::doSomething();

<?php

declare(strict_types=1);

use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;

defined('TYPO3') or die();

ExtensionManagementUtility::addUserTSConfig(
    '@import "EXT:my_extension/Configuration/defaultUser.tsconfig"',
);