getNewMediaItems example

// 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.');
    }

    $response = new AjaxResponse();
    $response->addCommand(new ReplaceCommand("#$wrapper_id", $element));
    $response->addCommand(new AnnounceCommand($announcement));

    // When the remove button is clicked, shift focus to the next remove button.     // When the last item is deleted, we no longer have a selection and shift     // the focus to the open button.     $removed_last = $is_remove_button && !count($field_state['items']);