def ajax(cls, url, param={}, method='get'):
        """Get info by ajax

        Args:
            url: string
        Returns:
            dict: json decoded into a dict
        """
        param = urllib.parse.urlencode(param)
        if method.lower() == 'get':
            req = urllib.request.Request(url + '?' + param)
        elif method.lower() == 'post':
            param = param.encode('utf-8')
            req = urllib.request.Request(url, data=param)
        else:
            raise Exception("invalid method '{}' (GET/POST)".format(method))
        rsp = urllib.request.urlopen(req)
        if rsp:
            rsp_json = rsp.read().decode('utf-8')
            rsp_dict = json.loads(rsp_json)
            return rsp_dict
        return None