Computed_field:8.x-2.0-alpha4.

needs-help.md

Code snippet tested.

$storage = \Drupal::entityManager()->getStorage("node");
$query = \Drupal::entityQuery('node');
$query->condition("type", $bundle);
$result = $query->execute();
foreach ($result as $nid) {
  $node = $storage->load($nid);
  $node->changed = REQUEST_TIME;
  $node->save();
}

how to batch update a computed field value for existed nodes? It works manually click save button on UI, but not work using code.