gistfile1.txt

  public function getUntransformedText(EntityInterface $entity, $field_name, $langcode, $view_mode) {
    $response = new AjaxResponse();

    // Direct text editing is only supported for single-valued fields.
    $field = $entity->getTranslation($langcode, FALSE)->$field_name;
    $editable_text = check_markup($field->value, $field->format, $langcode, FALSE, array(FILTER_TYPE_TRANSFORM_REVERSIBLE, FILTER_TYPE_TRANSFORM_IRREVERSIBLE));
    $response->addCommand(new GetUntransformedTextCommand($editable_text));

    return $response;
  }