What is the typescript type for next in socket IO middleware

[janusqa]

What is the typescript type for next in socket IO middleware

For example

export const chatAuthHandler = (socket:Socket, next) => {
	const data1 = socket.handshake.auth.data1 as string;
	check(data1)
		.then(() => next())
		.catch((_error) => next(new Error("Authentication Error")));
}

How would I type next.
Thanks in advance.

[davidtjones02]

For any future people curious, you can reference the implementation directly from the middleware definition.

At the current time of writing it the full type is:

use(fn: (socket: Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>, next: (err?: ExtendedError) => void) => void): this;

You can create a simple middleware type for this which will get the corresponding params. Similar approach can be used directly for middleware on the socket instance too.

import { Server } from "socket.io";

type MiddlewareFunction = Parameters<Server["use"]>[0];

export const chatAuthHandler: MiddlewareFunction = (socket, next) => {};

// elsewhere in your codebase
const io = new Server();

io.use(chatAuthHandler);