how to set different Node environment?

could some one tell tell how to set different environment for node app.

I've came across lots of documentation/tutorials but could'nt understand how to make use of it as am new to node. kindly give me some help to achieve this with below basic code.

i got below from some tutorial about how to create basic server. i want run this app based on different parameter am passing. feel quite difficult to set config file for this. for example i need run this based on different location

var express  = require('express');
var app      = express();
var port     = process.env.PORT || 3000;
var mongoose = require('mongoose');
var passport = require('passport');
var flash    = require('connect-flash');

var morgan       = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser   = require('body-parser');
var session      = require('express-session');

var configDB = require('./config/database.js');

var http = require('http').Server(app);


var MongoStore =  require('connect-mongo')(session);
mongoose.connect(some_db.url); 
mongoose.set('debug', false);
require('./config/passport')(passport); 


app.use(morgan('dev')); 
app.use(cookieParser()); 
app.use(bodyParser()); 

app.set('view engine', 'ejs'); 


app.use(session({
  store: new MongoStore({
    mongooseConnection: mongoose.connection /
  }),
  secret: 'screetservice',
  resave: true,
  saveUninitialized: true
}));

app.use(passport.initialize());
app.use(passport.session()); 
app.use(flash()); 

require('./app/routes.js')(app, passport, http); 

//app.use(express.static(__dirname + '/public'));
app.use('/static', express.static(__dirname + '/public'));
console.log("Server sees:"+__dirname + '/public');
app.use( express.static( "public" ) );
app.use( express.static( "./app/public" ) );


http.listen(port);
console.log('The magic happens on port ' + port);

many thanks for any help

via my_first_step