Returning/getting object from a module in nodejs mongodb

I am working on a nodejs app.
Folder structure is

app
app.js
package.json
../model/schema.js
../controller/controller.js
../views

All the logic is in controller.js while app.js performing routing itself....
I want to know how to get/return data(object) from controller.js to app.js.
I am using 'return' to send mongodb document from controller to app but its undefined.

Heres code of app.js..i have removed unneccessary code

  var express = require('express'),
   app = express.createServer(express.logger()),
   io = require('socket.io').listen(app),
   routes = require('./routes');
   var controller=require('./controller/controller');
   var model=require('./model/schema');

   app.get("/", function(req, res) {
     res.render("chatroom.html");
    });

   io.sockets.on('connection', function (socket) {
      socket.on('login',function(user)
      {
          var onliner=controller.loginUser(user);
          console.log("Onlinersss: ",onliner);
      });

      socket.on('registerUser',function(user){
          controller.registerUser(user);
      });
   });

Heres controller.js code:

  var model=require('../model/schema');
  exports.loginUser=function(user)
  {

      model.registerUser.findOne({uname:user.uname,pass:user.pass},function(err,doc){
        if(!err){ 
             console.log("Here loggedin: ",doc); 
             return doc;             
        }
        else
             console.log("Invalid username or password");
        });
  };