Create a room ID on the server side and join the client to it using sockets.io

I would like to create a random room ID on the server side and emit it to the client on connect, like below:

io.sockets.on('connection', function(socket){
    var roomID = Math.random().toString(36).substring(2, 13);  
    io.emit('message', roomID);
    socket.on('subscribe', function(room) { 
        socket.join(room); 
    })
});

Then, once the client has the server-created room ID, I would like to join the client to that room.

 var socket = io.connect();
 var lobby;
 socket.on('message', function (data) {
    lobby=data;
 });

 socket.emit('subscribe', lobby);

The problem is that I'm not able to pull the lobby variable out of the socket.on() function. Which, if I understand correctly, is because it's inside the anonymous function, and that makes it asynchronous.

Is there any solution here, or am I stuck with joining a room by giving it a name on the client side?

via Dshiz