colyseus.js: react-native colyseus.js 0.11.0 error

package.json …

"dependencies": {
    "buffer": "^5.4.0",
    "colyseus.js": "^0.11.0",
    "react": "16.8.6",
    "react-native": "0.60.5"
  },

…

import React, { Component } from 'react';
//import Board from './Board';
//import './css/board.css';
import * as Colyseus from "colyseus.js";
import { AsyncStorage, View, Text } from 'react-native';

import { Buffer } from "buffer";
window.localStorage = AsyncStorage;
global.Buffer = Buffer;


export default class Game extends Component {

    constructor(props) {
        super(props);

        this.colyseus = new Colyseus.Client('ws://31.173.240.80:2567')
        this.colyseus.joinOrCreate("gamebot")

/*
        this.colyseus.joinOrCreate("gamebot").then(room => {
            console.log("joined successfully", room);
        }).catch(e => {
            console.error("join error", e);
        });
*/