node socket app new instance scope

it is a simple socket app using event base pattern

const invitation = require('./invitation');
module.exports = function(io){
    io.on('connection', (socket)=>{
        var prepareGame = new PrepareGame(socket)
        socket.on("sendInvitation",(data, ack)=>{
            prepareGame.sendInvitation(data,ack)
        });
    });
}

and in prepareGame.js

const events = require('events');
const util = require('util');

class PrepareGame extends events {
    constructor(socket) {
        super();
        this.user = socket.user
        var self = this

        draftInvitation(data){
            this.newInvitation = {
                from_user: self.user.id,
                to_user: data.to_user,
                message:data.message,
                created_at:moment().unix(),
            }
            return this
        };

        self.on("toSocket", (eventName, clientId, data) => {
            console.log(` ===>>>> sending to listener ${eventName}`, clientId);
            var client  = users[clientId]
            if(client)
                client.emit(eventName, data)
        });

    }

    // public function
    sendInvitation(data, ack) {
        // console.log(this);
        var self = this
        data.message = 'New Invitation'
        draftInvitation(data)
        .emit("toSocket", "getInvitation", data.to_user, self.newInvitation)

        setTimeout(()=>{
            data.message = 'Invitation timeout'
            draftInvitation(data)
            .emit("toSocket", "getInvitation", self.user.id, self.newInvitation)
        }, 15000)

        if(typeof ack == 'function')
            ack({
                status:200,
                message: "invitation sent",
            })
    }
}

util.inherits(PrepareGame, events.EventEmitter )

module.exports =  PrepareGame

code is sum of different design pattern. it's working fine but I've some queries

1. io.connection called once to connect to socket and prepareGame instance created. considering two instance for two user then how sendInvitation automatically bound correct instance when calling
2. what happen with new prepareGame instance when socket disconnect ?
3. i want to remove (data, ack)=>{ } encloser from socket.on mean it should socket.on ("sendInvitation",prepareGame.sendInvitation) then how to manage this reference in sendInvitation function