Adding a custom DataType to Feed Me for CraftCMS

CustomJsonDatatype.php

<?php

namespace modules\datatypes;

use craft\feedme\datatypes\Json;
use illuminate\Support\Collection;

class CustomJsonDatatype extends Json
{
    /**
     * @var string
     */
    // This will be the name of the Feed Type visible when setting up the feed
    public static string $name = 'Custom JSON';
    
    // Public Methods
    // =========================================================================

    /**
     * @inheritDoc
     */
    public function getFeed($url, $settings, bool $usePrimaryElement = true): array
    {
        // Get the feed from the parent class
        $feed = parent::getFeed($url, $settings, $usePrimaryElement);

        // Map over the data key with our custom transformer method
        $feed['data'] = collect($feed['data'])
            ->map(function($item) {
                return $this->transformItem(collect($item));
            })
            ->toArray();
        return $feed;
    }
    
    public function transformItem(Collection $item): ?Collection
    {
        // do whatever you want here to each item
        if ($item->Category) {
            $values = collect(explode('|', $item->Category));
            $item->put('Category', $values->map(fn($value) => trim($value))->toArray());
        }
        
        return $item;
    }
}

Module.php

<?php

namespace modules;

use Craft;
use craft\feedme\events\RegisterFeedMeDataTypesEvent;
use craft\feedme\services\DataTypes;
use modules\datatypes\CustomJsonDatatype;
use yii\base\Event;
use yii\base\Module as BaseModule;

class Module extends BaseModule
{
    public function init(): void
    {
        Craft::setAlias('@modules', __DIR__);

        parent::init();

        Craft::$app->onInit(function() {
            $this->registerFeedMeDataTypes();
        });
    }
    
    private function registerFeedMeDataTypes(): void
    {
        // see https://docs.craftcms.com/feed-me/v4/developers/data-types.html#the-registerfeedmedatatypes-event
        Event::on(
            DataTypes::class,
            DataTypes::EVENT_REGISTER_FEED_ME_DATA_TYPES,
            static function(RegisterFeedMeDataTypesEvent $e) {
                $e->dataTypes[] = CustomJsonDatatype::class;
            }
        );
    }
}