book_node_load

book_node_load($nodes)

function book_node_load($nodes) {
  /** @var \Drupal\book\BookManagerInterface $book_manager */
  $book_manager = \Drupal::service('book.manager');
  $links = $book_manager->loadBookLinks(array_keys($nodes), FALSE);
  foreach ($links as $record) {
    $nodes[$record['nid']]->book = $record;
    $nodes[$record['nid']]->book['link_path'] = 'node/' . $record['nid'];
    $nodes[$record['nid']]->book['link_title'] = $nodes[$record['nid']]->label();
  }
}