Http call

Future<String> postData(String jsonData, String url) {
        var _completer = new Completer<String>();

        HttpRequest request = new HttpRequest(); // create a new XHR

        // POST the data to the server
        request.open("GET", url);
        request.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
        request.send(jsonData); // perform the async POST

        request.onReadyStateChange.listen((_) {
             if (request.readyState == HttpRequest.DONE)
                 if(request.status != 200 && request.status != 0) {
                      var json = JSON.decode(request.responseText);
                     _completer.completeError(json["errors"][0]["title"]);
                 } else {
                     _completer.complete(request.responseText);
                 }
         });

        return _completer.future;
    }