use Symfony\Component\HttpFoundation\JsonResponse;

/**
 * Class JsonApiArticlesController
 * @package Drupal\mymodule\Controller
 */
class JsonApiArticlesController {

  /**
   * @return JsonResponse
   */
  public function index() {
    return new JsonResponse([ 'data' => $this->getData(), 'method' => 'GET', 'status'=> 200]);
  }

  /**
   * @return array
   */
  public function getData() {

    $result=[];
    $query = \Drupal::entityQuery('node')
      ->condition('type', 'article')
      ->sort('title', 'DESC');
    $nodes_ids = $query->execute();
    if ($nodes_ids) {
      foreach ($nodes_ids as $node_id) {
        $node = \Drupal\node\Entity\Node::load($node_id);
        $result[] = [
          "id" => $node->id(),
          "title" => $node->getTitle(),
        ];
      }
    }
    return $result;
  }
}

use Symfony\Component\HttpFoundation\JsonResponse;

// if you know the data to send when creating the response
$response = new JsonResponse(['data' => 123]);

// if you don't know the data to send or if you want to customize the encoding options
$response = new JsonResponse();
// ...
// configure any custom encoding options (if needed, it must be called before "setData()")
//$response->setEncodingOptions(JsonResponse::DEFAULT_ENCODING_OPTIONS | \JSON_PRESERVE_ZERO_FRACTION);
$response->setData(['data' => 123]);

// if the data to send is already encoded in JSON
$response = JsonResponse::fromJsonString('{ "data": 123 }');