Defining and joining Socket.IO rooms

Within namespaces, you can define rooms or channels that a socket can join and leave.

By default, a room is created with a random un-guessable ID for the connected socket:

io.on('connection', (socket) => { 
    console.log(socket.id) // Outputs socket ID 
}) 

On connection, when emitting an event, for example:

io.on('connection', (socket) => { 
    socket.emit('say', 'hello') 
}) 

What happens underneath is similar to this:

io.on('connection', (socket) => { 
    socket.join(socket.id, (err) => { 
        if (err) { 
            return socket.emit('error', err) 
        } 
        io.to(socket.id).emit('say', 'hello') 
    }) 
}) 

The join method was used to include the socket inside a room. In this case, the socket ID is the joint room, and the only...