Implement notification system using node.js,express,socket

I just did something similar and handled it like this:

io.js - central node.js file where I handle new connnections and store io

var io = require('socket.io')();

io.on('connection', function(socket){
 console.log("Socket established with id: " + socket.id);

 socket.on('disconnect', function () {
  console.log("Socket disconnected: " + socket.id);
 });

});

module.exports = io;

someroute.js - somewhere in the node.js server application I want to emit messages

var appRoot = require('app-root-path');
var io = require(appRoot + '/server/io');

/*your code, somwhere you will call the
 * function below whenever you want to emit
 * the 'user_did_action' event:
*/
if(user.didNewStuff()){
 emitUserAction(user);
}

var emitUserAction = function(user){
  io.sockets.emit('user_did_action', user);
};

client_javascript.js - some client js (in my case angular, but it doesent matter), import the socket.io lib, then access somewhere in the client like this:

/*connect to the server*/
var socket = io.connect();

/*do something wen the event 'user_did_action'
 * is received, just invoke the callback
 *
 *in the function param data, you will have the same
 *data you emitted earlier in the server, 
 *in this example the user object!*/
socket.on('user_did_action', myFunctionToHandleTheEvent(data));