How to get node's view mode in hook_page_attachments?

Question

I need to get the node's view mode so that in the mymodule_page_attachments, I can add libraries conditionally if the node's view mode is set to full or default. I tried the following but not able to get the nodes view mode once I retrieve the$node` object.

How to get node's view mode in hook_page_attachments?

Here is what we tried:

function mymodule_page_attachments(array &$attachments) {
  $node = \Drupal::routeMatch()->getParameter('node');
  if(is_object($node)) {
     // we tried printing but that didn't result any view_mode field. 
     ksm($node);

    // Goal
    if($node['view_mode'] == 'full' or $node['view_mode'] == 'default') {
       // proceed with my logic. 
    }
  }
}

Answer 1

To attach a library only when a node in a certain view mode is displayed you can use hook_entity_view/hook_ENTITY_TYPE_view like following.

/**
 * Implements hook_ENTITY_TYPE_view().
 */
function MYMODULE_node_view(array &$build, \Drupal\Core\Entity\EntityInterface $entity, \Drupal\Core\Entity\Display\EntityViewDisplayInterface $display, $view_mode) {

  $node = $entity;
  if ($node->bundle() === 'page') {
    if ($view_mode === 'full') {
      $build['#attached']['library'][] = 'MYMODULE/foo';
    }
    elseif ($view_mode === 'default') {
      $build['#attached']['library'][] = 'MYMODULE/bar';
    }
  }
}

Answer 2

Drupal does not distinct between full and default here. If no full viewmode is given for a certain node type than the default viewmode is used. So you could check whether a given node type implements the full viewmode and apply your conditional logic based on this, like this:

function hook_page_attachments(array &$attachments) {
  /* @var \Drupal\node\Entity\Node $node */
  $node = \Drupal::routeMatch()->getParameter('node');
  if($node) {
    $view_modes = \Drupal::service('entity_display.repository')->getViewModeOptionsByBundle('node', $node->bundle());
    if (isset($view_modes['full'])) {
      // this is full
    }
    else {
      // this is default
    }
  }
}