Node.js - Socket.io client file not being served by basic node web server

I m very new to Node.js and Socket.io. I have built a very basic web server however when using it, I am unable to load the socket.io client file (I get a 404).

I am trying to use this client side code:

<script src="/socket.io/socket.io.js"></script>

My understanding is that Node should pick this up and resolve it? It does on a much simpler web server example.

My web server example where it is NOT resolved is as follows:

var server = http.createServer(function (request, response) {

    console.log('request starting...');

    var filePath = '.' + request.url;
    if (filePath == './')
        filePath = './index.html';

    var extname = path.extname(filePath);
    var contentType = 'text/html';
    switch (extname) {
        case '.js':
            contentType = 'text/javascript';
            break;
        case '.css':
            contentType = 'text/css';
            break;
    }

    path.exists(filePath, function(exists) {

        if (exists) {
            fs.readFile(filePath, function(error, content) {
                if (error) {
                    response.writeHead(500);
                    response.end();
                }
                else {
                    response.writeHead(200, { 'Content-Type': contentType });
                    response.end(content, 'utf-8');
                }
            });
        }
        else {
            response.writeHead(404);
            response.end();
        }
    });

My web server code where it DOES resolve is as follows:

app.listen(8080);

function handler (req, res) {
  fs.readFile(__dirname + '/index.html',
  function (err, data) {
    if (err) {
      res.writeHead(500);
      return res.end('Error loading index.html');
    }

    res.writeHead(200);
    res.end(data);
  });
}

Can anyone advise on what is causing it not serve the socket.io file on the client using the first web server example?

Best regards, Ben.