Wrong extentions property type

[dcharbonnier]

The extension property of the client return an object, the websocket api expect a string.

ws/lib/WebSocket.js

Line 53 in 4e7d48a

this.extensions = {};

MDN documentation

Attribute	Type	Description
Extensions	DOMString	The extensions selected by the server. This is currently only the empty string or a list of extensions as negotiated by the connection.

[lpinca]

We try to emulate the browser interface but in this case I don't see a reason to use a string.
We could use a private property for the extensions map and make extensions a getter.

get extensions () {
  return Object.keys(this._extensions).join(',');
}

but again I don't see any real advantage.

[dcharbonnier]

I agree it's not so important for this property but in general I find it very interesting to have ws that implements Websocket as much as possible and it's already the case 👍
const ws: typeof WebSocket = typeof (WebSocket) !== "undefined" ? WebSocket : require("ws");

Making this a getter would make ws behave like the WebSocket specifications from what I know and I could remove one test here https://github.com/dcharbonnier/advanced-websocket/blob/develop/src/Waterfall.ts#L49

Was just to let you know, feel free to close it if you want.

[lpinca]

I see, feel free to open a PR.