У вашего броузера проблема в совместимости с HTML5
The websocket server is run in the NodeMCU and its code is based on one of the examples provided in the arduinoWebsocket project.
The client is a QML application that can be executed in a desktop PC or a smartphone.
Find more about this at http://www.deuteros.es/blog/125-an-easy-example-of-websockets-with-a-nodemcu-esp8266-an-rgb-led-and-qt