Element.php

<?php
namespace Bitrix\Iblock\Controller;
 
use Bitrix\Iblock\IblockTable;
use Bitrix\Main\Application;
use Bitrix\Main\DI\ServiceLocator;
use Bitrix\Main\Engine\Contract\FallbackActionInterface;
use Bitrix\Main\Engine\Controller;
 
final class Element extends Controller implements FallbackActionInterface
{
    protected $iblock;
 
    protected function getDefaultPreFilters()
    {
        return [];
    }
 
    public function fallbackAction($actionName)
    {
        $this->setSourceParametersList(array_merge(
            $this->getSourceParametersList(), [['iblock' => $this->getIblock()]]
        ));
 
        return $this->forward($this->getController(), $actionName);
    }
 
    protected function getController()
    {
        $iblock = $this->getIblock();
 
        $serviceLocator = ServiceLocator::getInstance();
        $serviceId = "iblock.element.{$iblock->getApiCode()}.rest.controller";
 
        if ($serviceLocator->has($serviceId))
        {
            // get from service locator
            $controller = $serviceLocator->get($serviceId);
        }
        else
        {
            $controller = DefaultElement::class;
        }
 
        return $controller;
    }
 
    protected function getIblock()
    {
        if ($this->iblock === null)
        {
            $iblockId = Application::getInstance()->getContext()->getRequest()->get('iblockId');
 
            $this->iblock = IblockTable::getByPrimary($iblockId, [
                'select' => ['ID', 'API_CODE']
            ])->fetchObject();
        }
 
        return $this->iblock;
    }
}