send functions should have generic types

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

Currently functions like emit are not typable:

socket.emit('my-event-name', dto);

This applies to both socket.io server and client.

Describe the solution you’d like I would like to have generic types on all emit functions to (optionally) type the send-object and the response-object:

socket.emit<void, MyDtoInterface>('my-event-name', dto);
socket.emit<MyResponseDtoInterface, MyDtoInterface>('my-event-name', dto, responseDto => {
   // ...
});

Now if an interface changes TypeScript throws an error if the objects are not updated.

Suggested solution Functions could look something like this:

// Server:
emit<TInput = any>(ev: string, data: TInput);

// Client:
emit<TResult = any, TInput = any>(ev: string, data: TInput, (response: TResult) => {});

[MaximeKjaer]

I have a WIP implementation that would fix this issue on this branch. @darrachequesne would there be interest in potentially merging something like that? If so, I can complete the implementation.

The implementation adds two optional type parameters to Socket, Server and Namespace. These type parameter are a mapping of event names to listener types; by default, it’s a mapping of all strings to (...args: any[]) => void, so it retains the current behavior if no type parameters are passed. However, users can optionally pass a mapping of their event names to the types of the listeners that listen to those events.

[MickL]

For example Angular http client does it like this:

https://github.com/angular/angular/blob/2c757591ee334ced115bc93ba1b944803bb0c07e/packages/common/http/src/client.ts#L2291

Or all NestJS Microservice Clients: https://github.com/nestjs/nest/blob/eb239abd8261b3328945865790ffc3c377b60827/packages/microservices/client/client-proxy.ts#L60

I specifically used NestJS as the source of my proposal above.

It is easy to implement two generics, it does not add any extra code and is totally optional to use.