server.js

const Connected = {};

function removeUser(conferenceId, uid, ws)
{
    const Conf = Connected[conferenceId];
    const a = Conf[uid];
    if (a.length == 1) {
        if (Conf.numParticipants == 1) {
            delete Connected[conferenceId];
        } else {
            delete Conf[uid];
            Conf.numParticipants--;
        }
    } else {
        a.splice(a.indexOf(ws), 1);
    }
}

function addUser(conferenceId, uid, ws) {
    var Conf = Connected[conferenceId];
    if (!Conf) {
        Conf = {}
        Conf.numParticipants = 0;
        Connected[conferenceId] = Conf;
    }
    if (!Conf[uid]) {
        Conf[uid] = [ws];
    } else {
        Conf[uid].push(ws);
    }
    Conf.numParticipants++;
    return Conf;
}

app.ws("/conf", (ws, req) => {
        console.log(req.query);
        const conferenceId = req.query.conferenceId;
        const idToken = req.query.idToken;
        return idTokenToUid(idToken).then(uid => {
                ws.on("close", () => {
                        removeUser(conferenceId, uid, ws);
                    });
                const Conf = addUser(conferenceId, uid, ws);
                ws.on("message", msg => {
                        for (var user in Conf) {
                            if (user === "numParticipants") continue; // hack                                                                                                  
                            Conf[user].map(to_ws => {
                                    if (to_ws != ws) {
                                        try {
                                            to_ws.send(msg);
                                        } catch (err) {
                                            console.log(err);
                                            removeUser(conferenceId, uid, to_ws);
                                        }
                                    }
                                });
                        }
                    });

            });
    });