node.js - Socket IO The connection to ws://someAddress was interrupted while the page was loading

I am trying to follow along with a simple example of Socket.IO located at http://socket.io/get-started/chat/. So far I have the following code in my index.js file:

// INDEX.JS File

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function (req, res) {
    res.sendfile('index.html');
});


io.on('connection', function (socket) {
    socket.on('chat message', function (msg) {
        console.log('message: ' + msg);
    });
});
http.listen(3000, function () {
    console.log('listening on *:3000');
});

The error I am getting is:

The connection to ws://localhost:3000/socket.io/?EIO=2&transport=websocket&sid=i0SyiRvHJC1GUiafAAAC was interrupted while the page was loading.

I'm using FireFox to browse the page. It also doesn't work in Chrome.

Answer

Taking exactly your example works fine for me. I do get an error but not the same you are indicating (which is fine since this session does not exist here):

{
  code: 1,
  message: "Session ID unknown"
}

Is the index.html in the right path (visible by your app)?