Change MessageEvent to Event like the spec.

[Et7f3]

Source https://html.spec.whatwg.org/multipage/indices.html#event-open

I don't know the type of close event for websocket https://html.spec.whatwg.org/multipage/indices.html#event-error

Here is the source: https://html.spec.whatwg.org/multipage/web-sockets.html#feedback-from-the-protocol (scroll up a bit)
Also for message event the spec say any but MDN in french say

DOMString, Blob ou un tableau ArrayBuffer

https://developer.mozilla.org/fr/docs/Web/API/MessageEvent#Properties

Should I had a classify function or it should be treated in userland ? From my test I receive only string.
I have received a Blob after sending a ArrayBuffer to https://www.websocket.org/echo.html.

[Et7f3]

readyState prop could be of type readyState because it is just a mapping with the same order. I kept the raise if n > 3 (this should be the case if more state are added). I think it will unlikely happen but it is a living standard so I think it is fine.