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$node = \Drupal::entityManager()->getStorage('node')->load($nodeid);

$view_builder = \Drupal::entityManager()->getViewBuilder('node');

$render = $view_builder->view($node, 'full');
//or
$render = $view_builder->viewMultiple($nodes, 'full');

$html = \Drupal::service('renderer')->renderRoot($render);