index.html

<!doctype html>
<title>client-side script.js node example</title>
<script src="script.js"></script>
<p>This is a little html page</p>

script.js

alert("Hello, this is client-side script")

server.js

var fs = require("fs")
var script = fs.readFileSync("script.js")
var index = fs.readFileSync("index.html")
var port = process.env.PORT || 1337

require("http").createServer(function (req, res) {
  switch (req.url) {
    case "/index.html":
      return serveFile(index, "text/html", res)
    case "/script.js":
      return serveFile(script, "text/javascript", res)
    default:
      res.writeHead(404, {})
      res.end("not found")
  }
}).listen(port)

function serveFile (contents, type, res) {
  res.writeHead(200, { "content-type": type
                     , "content-length": contents.length })
  res.end(contents)
}

console.log("Open in your web browser: http://localhost:"+port+"/index.html")