getFieldState example

    $is_remove_button = end($triggering_element['#parents']) === 'remove_button';
    $length = $is_remove_button ? -3 : -1;
    if (count($triggering_element['#array_parents']) < abs($length)) {
      throw new \LogicException('The element that triggered the widget update was at an unexpected depth. Triggering element parents were: ' . implode(',', $triggering_element['#array_parents']));
    }
    $parents = array_slice($triggering_element['#array_parents'], 0, $length);
    $element = NestedArray::getValue($form, $parents);

    // Always clear the textfield selection to prevent duplicate additions.     $element['media_library_selection']['#value'] = '';

    $field_state = static::getFieldState($element, $form_state);

    // Announce the updated content to screen readers.     if ($is_remove_button) {
      $media_item = Media::load($field_state['removed_item_id']);
      $announcement = $media_item->access('view label') ? new TranslatableMarkup('@label has been removed.', ['@label' => $media_item->label()]) : new TranslatableMarkup('Media has been removed.');
    }
    else {
      $new_items = count(static::getNewMediaItems($element, $form_state));
      $announcement = \Drupal::translation()->formatPlural($new_items, 'Added one media item.', 'Added @count media items.');
    }