Uninstall and cleanup hooks in Wordpress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when the uninstall.php file is missing in a plugin?

In WordPress, a plugin uses an uninstall.php file to clean up data when uninstalled. What happens if this file is missing and the plugin is uninstalled?

A No cleanup code runs automatically; plugin data remains in the database.

B WordPress will run the uninstall hook registered in the main plugin file instead.

C WordPress throws an error and prevents uninstallation.

D WordPress deletes all plugin data automatically without any code.

💡 Hint

Think about what WordPress does by default without explicit uninstall instructions.

If the uninstall.php file is missing and no uninstall hook is registered, WordPress does not run any cleanup code automatically. Plugin data remains in the database until manually removed.

📝 Syntax

intermediate

Which uninstall hook registration is correct?

You want to register an uninstall hook in your main plugin file to clean up options. Which code snippet correctly registers the uninstall hook?

A register_hook('uninstall_plugin', 'my_plugin_cleanup');

B add_action('uninstall', 'my_plugin_cleanup');

C add_uninstall_hook('my_plugin_cleanup');

D register_uninstall_hook(__FILE__, 'my_plugin_cleanup');

💡 Hint

Look for the exact WordPress function name and parameters.

The correct function to register an uninstall hook is register_uninstall_hook with the plugin file path and callback function.

🔧 Debug

advanced

Why does the uninstall hook not run when uninstalling the plugin?

Consider this uninstall.php file content:

if (!defined('WP_UNINSTALL_PLUGIN')) {
    exit();
}

delete_option('my_plugin_option');

Why might the uninstall hook not run when uninstalling the plugin?

Wordpress

if (!defined('WP_UNINSTALL_PLUGIN')) {
    exit();
}

delete_option('my_plugin_option');

A The delete_option function is misspelled, causing a fatal error.

B The constant WP_UNINSTALL_PLUGIN is not defined during uninstall, so the script exits early.

C The uninstall.php file is not in the plugin root folder, so WordPress does not find it.

D The uninstall hook requires a function wrapper around delete_option to run.

💡 Hint

Check the file location and how WordPress detects uninstall.php.

WordPress only runs uninstall.php if it is located in the root folder of the plugin. If placed elsewhere, it won't run and no cleanup happens.

❓ state_output

advanced

What is the state of options after uninstall hook runs?

A plugin registers this uninstall hook:

function cleanup() {
    delete_option('plugin_setting');
    delete_option('plugin_cache');
}
register_uninstall_hook(__FILE__, 'cleanup');

After uninstalling the plugin, what happens to these options?

Wordpress

function cleanup() {
    delete_option('plugin_setting');
    delete_option('plugin_cache');
}
register_uninstall_hook(__FILE__, 'cleanup');

A Both options remain because delete_option only works during plugin activation.

B Both 'plugin_setting' and 'plugin_cache' options are removed from the database.

C Only 'plugin_setting' is removed; 'plugin_cache' remains.

D Neither option is removed because uninstall hooks do not delete options.

💡 Hint

Think about what delete_option does and when uninstall hooks run.

The uninstall hook runs the cleanup function which calls delete_option on both options, removing them from the database.

🧠 Conceptual

expert

Why use uninstall.php instead of register_uninstall_hook?

Which reason best explains why a plugin developer might prefer using an uninstall.php file over register_uninstall_hook for cleanup?

A uninstall.php runs even if the plugin is deleted without deactivation, ensuring cleanup always happens.

B register_uninstall_hook runs faster and is preferred for performance reasons.

C uninstall.php allows cleanup code to run during plugin activation as well.

D register_uninstall_hook requires the plugin to be active, so uninstall.php is used for inactive plugins.

💡 Hint

Consider when uninstall.php is triggered compared to uninstall hooks.

uninstall.php is executed when the plugin is deleted directly, even if not deactivated first, ensuring cleanup always runs.