Manually add types to `socket.data`

[T-Damer]

Is your feature request related to a problem? Please describe.

I was working with socket.data and noticed that I couldn't define its types. I tried to search the same issue here, but didn't find

Describe the solution you'd like

• For example I want to do socket.data<User>
• or maybe pass it when server is being created:

new Server<{user: User}>(server, { cors: { origin: * }, })

• Or maybe inherit types from usage socket.data = user then socket.data becomes socket.data: {User, ...any} or something like this

Describe alternatives you've considered

Right now I can create a subclass to use it:

interface SocketDataType = { user: User }

export declare class ExtendedSocketServer<ListenEvents extends EventsMap = DefaultEventsMap, EmitEvents extends EventsMap = ListenEvents, ServerSideEvents extends EventsMap = DefaultEventsMap, SocketDataType = any> extends Server<ListenEvents, EmitEvents, ServerSideEvents> {
  of(name: string | RegExp | ParentNspNameMatchFn, fn?: (socket: ExtendedSocketServer<ListenEvents, EmitEvents, ServerSideEvents, SocketDataType>) => void): Namespace<ListenEvents, EmitEvents, ServerSideEvents>;
}

Additional context

Also, I can use the patch-package. I just modified the original node_modules/socket.io/dist/socket.d.ts and run yarn patch-package

[darrachequesne]

That sounds reasonable 👍 would you have time to open a pull request for this?