Why Nothing display script with node js and html

in the script html and node js when i run this i get the display i get notthing display

var http = require('http');
http.createServer(function(req, res) {
    var html = buildHtml(req);
    res.writeHead(200, {
        'Content-Type': 'text/html',
        'Content-Length': html.length,
        'Expires': new Date().toUTCString()

function buildHtml(req) {
    var header = '';
    var body = '<h1>Node.js Tutorial</h1><p>We are learning http module</>';
    return '<!DOCTYPE html>' + '<html><header>' + header + '</header><body>' + body + '</body></html>';