Setting Socket.io room variables

Socket.io made some breaking changes in the newest version and rooms cannot be accessed like they used to. It changed a lot of objects and arrays into Maps and Sets, you can see it in the logs you've posted.

Set objects are collections of values. You can iterate through the elements of a set in insertion order. A value in the Set may only occur once; it is unique in the Set's collection.

The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.

Accessing properties of a Map works differently than accessing properties of a normal Object. Example:

const myMap = new Map();
myMap.set("foo", "bar");
console.log(myMap["foo"]) // undefined
console.log(myMap.get("foo")) // bar

Same applies to Sets, however in your case querying this Set in particular is probably a wrong approach, as this set only holds a collection of ids, and not actual room objects. Even if you were to get a value out of the Set, you could not access it's properties (host, isOpen and players) since it is only a string.

The version 3.0 made accessing the list of all rooms directly impossible I'm afraid. However the adapter now has a property socketRooms, which can be used in place of it.

In order to access rooms of a socket easier, you should access them like so:

io.sockets.adapter.socketRooms(socketId);

However that would still just return a list of strings.

The simplest solution to this problem would be to create an external variable outside of the connection scope.

const rooms = {};

io.on('connection', (socket, next) => {
    socket.on('create game', async () => {
        console.log('Creating game...');
        socket.username = await generateUsername();

        socket.roomId = generateId();

        socket.join(socket.roomId);

        if (!rooms[socket.roomId]) rooms[socket.roomId] = {};
        rooms[socket.roomId].host = socket.username;
        rooms[socket.roomId].isOpen = true;
        rooms[socket.roomId].players = [socket.username];

        console.log('Game created! ID: ', socket.roomId);
    });
}

As you can see in your own log, io.sockets.adapter.rooms is a Map object (in the later versions of socket.io), not a plain object. That means that a room is accessed with .get(), not with plain indexing such as what you are using:

io.sockets.adapter.rooms[socket.roomId].host = socket.username;

That simply won't work because there is no plain socket.roomId property on the Map.

If you wanted to get the room object, you would have to do this:

let roomObj = io.sockets.adapter.rooms.get(socket.roomId);
roomObj.host = socket.username;

In my opinion, I wouldn't mess with the room objects directly. We already know that socket.io has changed their design before, rendering any code that tried to use them as broken and in need of redesign. Instead, I'd probably just create my own data structure where I stored my own data and then I won't be dependent upon the whims of how socket.io changes their design. Accessing the room objects directly is not a committed design or committed API of socket.io. They can change how it works whenever they want and have, indeed, changed it recently.

After the breaking update from Socket.io of changing Array to Map. A simple solution would be changing:

    io.sockets.adapter.rooms[socket.roomId].host = socket.username;

to:

    io.sockets.adapter.get(socket.roomId).host = socket.username;