How to: cacheable JSON response in Drupal 8, 9 & 10

In my book Learning Drupal as a framework, we learn some nice things about cacheable dependencies. Recently I had to provide a JSON controller with cached data. Here is an example:

<?php
namespace Drupal\platform_custom\Controller;

use Drupal\Core\Cache\CacheableJsonResponse;
use Symfony\Component\HttpFoundation\JsonResponse;
use Drupal\Component\Serialization\Json;

/**
 * Class PlatformJsonController
 * @package Drupal\platform_custom\Controller
 */
class PlatformJsonController {

  /**
   * @return JsonResponse
   */
  public function render() {
    $config = \Drupal::config('platform_custom.customconfig')->get('platform_data');
    $decoded = Json::decode($config);
    $response = new CacheableJsonResponse($decoded, 200);
    $response->addCacheableDependency(\Drupal::config('platform_custom.customconfig'));
    return $response;
  }

}

This JSON page will only invalidate its caches when the config gets changed in the back-end.