AliasLinkEnhancer.php

<?php

namespace Drupal\module_name\Plugin\jsonapi\FieldEnhancer;

use Drupal\Core\Url;
use Drupal\jsonapi_extras\Plugin\ResourceFieldEnhancerBase;
use Shaper\Util\Context;

/**
 * Use alias for internal link field value.
 *
 * @ResourceFieldEnhancer(
 *   id = "alias_link",
 *   label = @Translation("Alias for link (link field only)"),
 *   description = @Translation("Add alias for internal link field.")
 * )
 */
class AliasLinkEnhancer extends ResourceFieldEnhancerBase {

  /**
   * {@inheritdoc}
   */
  protected function doUndoTransform($data, Context $context) {
    if (isset($data['uri'])) {
      $url = Url::fromUri($data['uri']);
      $data['alias'] = $url->toString(TRUE)->getGeneratedUrl();
    }

    return $data;
  }

  /**
   * {@inheritdoc}
   */
  protected function doTransform($value, Context $context) {
    return $value;
  }

  /**
   * {@inheritdoc}
   */
  public function getOutputJsonSchema() {
    return [
      'type' => 'object',
    ];
  }

}