public function getAttr($attr)
    {
        $attributeValue = $this->con->evaluateJavascript(sprintf('%s.getAttribute(%s)', $this->getAccessor(), json_encode($attr)));

        if ($attributeValue === false) {
            // see https://github.com/kriswallsmith/Buzz/pull/138 bug
            return '';
        }

        return $attributeValue;
    }