How to serve external js file to node.js server

can you help me I downloaded the js file for socket.io browser client.and put it on a js folder...but I am having problem node.js doesn't serves me the external js

<script src="./js/socketio.js"></script>

how do I serve the external js file ?

Here is the app.js server code

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

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);
        });


}

io.on('connection', function (socket) {
    socket.emit('news', { hello: 'world' });
    socket.on('my other event', function (data) {
        console.log(data);
    });
});

Thank you in advance.