Please check http://procbits.com/connecting-to-a-sockjs-server-from-native-html5-websocket!
After you append /websocket (to your URL), it will give you the error
Failed to parse Origin header value [null]
😉
, which then will in turn lead you to that link.
You’ll have to add .setAllowedOrigins("*") to your addHandler() method, and then it could finally work!