Error when running page with mongo, node.js and socket.io - node.js

Question

I'm new to using mongo and having difficulties with set-up on local OSX server.
When I run node app.js my page appears on http://127.0.0.1:3000/ but I get this error:
Firefox can't establish a connection to the server at ws://127.0.0.1:3000/socket.io/?EIO=3&transport=websocket&sid=************. socket.io.js:5325:0
The connection to ws://127.0.0.1:3000/socket.io/?EIO=3&transport=websocket&sid=*************** was interrupted while the page was loading.
and when I refresh the page in firefox I get Unable to connect server at 127.0.0.1:3000. and the following error in terminal:
a user connected
/Users/******/express_intro/node_modules/mongodb/lib/url_parser.js:15
if(url.indexOf("mongodb://") != 0)
^
TypeError: Cannot read property 'indexOf' of undefined
at module.exports (/Users/******/express_intro/node_modules/mongodb /lib/url_parser.js:15:9)
at Function.MongoClient.connect (/Users/******/express_intro/node_modules/mongodb/lib/mongo_client.js:95:16)
at Namespace.<anonymous> (/Users/******/express_intro/app.js:48:8)
at Namespace.emit (events.js:107:17)
at Namespace.emit (/Users/******/express_intro/node_modules/socket.io/lib/namespace.js:205:10)
at /Users/******/express_intro/node_modules/socket.io/lib/namespace.js:172:14
at process._tickCallback (node.js:355:11)
Here is the app.js
var express= require('express');
var bodyParser=require('body-parser');
var path=require('path');
var app=express();
var mongo=require('mongodb').MongoClient;
var http = require('http'); //the variable doesn't necessarily have to be named http
//configure app
app.set('port',process.env.PORT || 3000);
app.set('view engine','jade');
app.set('views',path.join(__dirname,'views'));
//use middleware
app.use(express.static(path.join(__dirname,'public')));
app.use(bodyParser.urlencoded({ extended: true }));
//define routes
var todoItems=[
{id:1,desc:'foo'},
{id:2,desc:'bar'},
{id:3,desc:'baz'}
];
app.get('/',function(req,res){
res.render('index',{
title:'My App',
items:todoItems
});
});
var serve=http.createServer(app);
var io=require('socket.io')(serve);
serve.listen(app.get('port'), function(){
console.log('Ready on port ' + app.get('port'));
});
io.on('connection',function(socket){
console.log('a user connected');
mongo.connect(process.env.CUSTOMCONNSTR_MONGOLAB_URI,function(err,db){
if(err){
console.warn(err.message);
}
else{
var collection=db.collection('chat messages')
var stream=collection.find().sort().limit(10).stream();
stream.on('data',function(chat){
console.log('emitting chat');
socket.emit('chat',chat.content);
});
}
});
});
Here is the client code
//var socket=io();
var socket = io('http://localhost:3000/');
$('#send-message-btn').click(function(){
var msg=$('#message-box').val();
socket.emit('chat',msg);
$('#messages').append($('<p>').text(msg));
$('#message-box').val('');
return false;
});
socket.on('chat',function(msg){
$('#message').append($('<p>').text(msg));
});
I also get this on loading the page first time
Any help appreciated.
Thanks