javascript - nodejs express: store parameters in variable

I am still new with nodejs, still not sure how to access a variable in a function and call the variable back.

check few links: but im getting really confused. Please help!

Node.JS: How to pass variables to asynchronous callbacks?

How can we access variable from callback function in node.js?

var express = require('express');
var app = express();
var router = express.Router(); 
var https = require('https').createServer( ssl_options, app);
var io = require('socket.io')( https );
**var user_id;

var room_id;**

router.use(function(req, res, next) {
    next(); 
});

app.use('/chat',router);

router.route( '/chat/:user_id/:room_id' )
.get(function(req,res){


    res.sendFile( __dirname + '/index.html' );

    user_id = req.param('user_id');
    room_id = req.param('room_id');

});

https.listen(3000);


io.on('connection', function(socket){

  **console.log ( user_id );
  console.log ( room_id );**


});