// Define entity type to lookup.
$entity_type = 'node';
// Execute a query in order to retrieve an array of Article's ids.
$ids = \Drupal::entityQuery($entity_type)
->condition('type', 'article')
->execute();
/** @var \Drupal\node\NodeStorage $controller */
$controller = \Drupal::entityTypeManager()
->getStorage($entity_type);
/** @var \Drupal\node\Entity\Node[] $entities */
$entities = $controller->loadMultiple($ids);
// Deletes permanently saved entities.
$controller->delete($entities);