app.js

const express = require('express');
const app = express();
let http = require('http').Server(app);
let io = require('socket.io')(http);

const port = process.env.PORT || 3000;

app.use(express.static('public'));

http.listen(port, () => {
    console.log( "listening on port", port );
});

io.on('connection', socket => {
    console.log( 'a user connected' );

    socket.on('create or join', room => {
        console.log( 'create or join to room', room );
        const myRoom = io.sockets.adapter.rooms.get(room) || {size: 0};
        const numClients = myRoom.size;

        console.log( room, 'has', numClients, 'clients' );
        if (numClients === 0) {
            socket.join(room);
            socket.emit('created', room);
        }
        else if (numClients === 1) {
            socket.join(room);
            socket.emit('joined', room);
        }
        else {
            socket.emit('full', room);
        }

    });

    socket.on('ready', room => {
        socket.broadcast.to(room).emit('ready');
    });

    socket.on('candidate', event => {
        socket.broadcast.to(event.room).emit('candidate', event);
    });

    socket.on('offer', event => {
        socket.broadcast.to(event.room).emit('offer', event.sdp);
    });

    socket.on('answer', event => {
        socket.broadcast.to(event.room).emit('answer', event.sdp);
    });
});