Chrome Extension - node.js - Socket.io

Question

I'm trying make a chrome extension which shows a notification when I get a message from socket.io node.js server.

Can I firstly say I have looked around a lot; some people have had similar errors but I can't seem to understand the answers and how to correct them on my PC because mine may have a different layout. Talking individually like this is better in my opinion.

This is what I have in my directory extension entitled "Projects": My extension directory

In content.js : Uncaught ReferenceError: io is not defined

var socket = io.connect('http://localhost:1337');
socket.on("hello",function(data){
    console.log(data.text);
    chrome.runtime.sendMessage({msg:"socket",text:data.text},function(response){});
});

In manifest.json :

{
   "background": {
      "scripts": [ "background.js" , "socket.io.js"]
   },
   "content_scripts": [ {
      "js": [ "content.js" ],
  "matches": ["http://*/*", "https://*/*"]
   } ],
   "manifest_version": 2,
"version":"1",
   "name": "MyExtension"
}

In background.js :

chrome.runtime.onMessage.addListener(
    function(request,sender,senderResponse){
        if(request.msg==="socket"){
            console.log("receive from socket server: "+request.text);
        }
    }
);

And finally, app.js, my server :

var app = require('http').createServer(handler).listen(1337);
var io = require('socket.io').listen(app);

function handler(req,res){
    console.log(req.url);
    res.writeHead(200, {'Content-Type':'text/plain'});
    res.end('Hello Node\n You are really really awesome!');
}

io.sockets.on('connection',function(socket){
    socket.emit('hello',{text:"node!"});
});

This is what is inside node_modules. NOTE : THE ONLY NPM I HAVE INSTALLED IS SOCKET.IO Inside node_modules