use dokuwiki\Extension\ActionPlugin;
use dokuwiki\Extension\EventHandler;
use dokuwiki\Extension\Event;

class action_plugin_example extends ActionPlugin {

    /**
     * plugin should use this method to register its handlers 
     * with the dokuwiki's event controller
     */
    public function register(EventHandler $controller) {
        $controller->register_hook('AJAX_CALL_UNKNOWN', 'BEFORE', $this, 'ajaxCall');
    }
    
    /**
     * handle ajax requests
     */
    public function ajaxCall(Event $event) {
        if ($event->data !== 'plugin_example') {
            return;
        }
        //no other ajax call handlers needed
        $event->stopPropagation();
        $event->preventDefault();

        //e.g. access additional request variables
        global $INPUT;
        $name = $INPUT->str('name');
    
        //data
        $data = [];

        //set content type
        header('Content-Type: application/json');
        echo json_encode($data);
    }
}