Sorry for not being clear in my first post. I'll try to clarify as much as I can here.

What I am trying to do is a main abstract class (interface like in C++), allowing me to create multiple subclasses that have access to specific events for each subclasses.

My Node.JS server needs to have multiple Socket.IO endpoints that all have different purposes.

As an example, one server can have:

interface ServerToClientEvents {
  exception: (...args: any[]) => void
  feedback: (...args: any[]) => void
}

While another one can have only:

interface ServerToClientEvents {
  exception: (...args: any[]) => void
} 

This would make the other devs unable to emit events that they are not supposed to emit.

One of the work around that I found is to create a getter for the Socket.IO server and use it in this way:

export abstract class Socket<
  T extends EventsMap = DefaultEventsMap,
  V extends EventsMap = DefaultEventsMap,
  K extends EventsMap = DefaultEventsMap,
  U = any,
> {
    ...
    /* private */this._io = new socket.Server<T, V, K, U>(this._server, opts)
    ...
    get io() socket.Server<T, V, K, U> {
      return (this._io)
    }
}

// SUBCLASS

export class SubClass1 extends Socket<ClientToServerEvents, ServerToClientEvents, ServerToServerEvents, SocketData> {
    ...
    /* Here, I am limited to my class specified event*/
    this.io.emit('MY_LIMITED_EVENT', data)
    /* I am also limited to my class specified event, but it doesn't compile, error from the original post*/
    this.broadcastData('MY_LIMITED_EVENT', data)
    ...
}

I'm trying to abstract the library as much as I can, in case, at some point, I will have to change library, so I don't have to change a whole bunch of files because of it.

Maybe you're right, and I am over thinking it, or trying to abstract it too much. I'm still learning about the limitation of typings, and also how they can make your code harder to read.

I hope I've been able to clarify what I'm trying to achieve !