`SocketData` type is not passed down to the `Namespace`

[OrkhanAlikhanov]

SocketData type is not passed down to the Namespace when we do io.of().
That results in socket.data being any type:

Example:

const io = new Server<{},{},{},{ username: string }>()

io.on('connection', socket => {
   socket.data /// { username?: string }
})

io.of('/nps').on('connection', socket => {
   socket.data /// any
})

Source code:

socket.io/lib/index.ts

Lines 577 to 582 in 51784d0

	public of(
	name: string | RegExp | ParentNspNameMatchFn,
	fn?: (
	socket: Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>
	) => void
	): Namespace<ListenEvents, EmitEvents, ServerSideEvents> {

Should be:

of(...): Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>;

[OrkhanAlikhanov]

Also it would be nice to have RemoteSocket.data type safe. Right now it defaults to any

[darrachequesne]

@OrkhanAlikhanov that's a great idea! Would you have the time to open a pull request?

[OrkhanAlikhanov]

@darrachequesne When making RemoteSocket.data type safe, should BroadcastOperator<EmitEvents> also change to BroadcastOperator<EmitEvents, SocketData>? I ask because BroadcastOperator.fetchSockets is the method that returns RemoteSocket.

There are 2 options:

1. Make BroadcastOperator like BroadcastOperator<EmitEvents, SocketData = any>.
2. Only update fetchSockets method signature:

//from
fetchSockets(): Promise<RemoteSocket<EmitEvents>[]>
// to
fetchSockets<SocketData = any>(): Promise<RemoteSocket<EmitEvents, SocketData>[]>

I think it's better to go with second option. I don't see need to pass SocketData around BroadcastOperator