为什么Node.js应用程序只能从127.0.0.1/localhost访问？

我是关于教我的朋友介绍节点,但后来我想知道为什么这个代码来自nodejs.org:

var http = require('http');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello World\n');
}).listen(80, '127.0.0.1');
console.log('Server running at http://127.0.0.1:80/');

托管时,它无法从公共IP访问(它仍然可以从localhost访问),而来自express.js的代码:

var express = require('express');
var routes = require('./routes');
var user = require('./routes/user');
var http = require('http');
var path = require('path');

var app = express();

// all environments
app.set('port', process.env.PORT || 80);
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');
app.use(express.favicon());
app.use(express.logger('dev'));
app.use(express.json());
app.use(express.urlencoded());
app.use(express.methodOverride());
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));

// development only
if ('development' == app.get('env')) {
  app.use(express.errorHandler());
}

app.get('/', routes.index);
app.get('/users', user.list);

http.createServer(app).listen(app.get('port'), function(){
  console.log('Express server listening on port ' + app.get('port'));
});

确实.请帮我修改nodejs主页上的基本代码,以便从公共IP访问它,这样我就可以以非常基本的方式向我的朋友展示它.express.js生成的新代码工作得很好.

我在这里错过了什么？