anchor.diff:            int pos = messageFile.name.indexOf('.');
             filename = 'HackMessage' + messageFile.name.substring(pos);
             print(filename);
  +        } else {
  +          querySelector('#form-error-alert').classes.remove('disappear');
  +          return new Future.value(null);
           }
           break;
       }
  -    uploadMsg(userName, userEmail, receiverName, receiverEmail, isFile, message, messageFile, filename)
  +    return uploadMsg(userName, userEmail, receiverName, receiverEmail, isFile, message, messageFile, filename)
       .then((_) {
         window.location.href = '../authen_done';
       })
  
positive.code:     switch(messageInput.type) {
        case 'text':
          message = messageInput.value;
          break;
        case 'file':
          isFile = true;
  
negative.code: library client.authen;
  
  import 'dart:html';
  import 'dart:async';
  import 'package:StupidBirdExpress/client/parse.dart';
  
  void main() {
  