Express.js - app.listen vs server.listen

Question

This may be a very basic question but I simply don't get it. What is the difference between creating an app using Express.js and starting the app listening on port 1234, for example:

var express = require('express');
var app = express();

//app.configure, app.use etc

app.listen(1234);

and adding an http server:

var express = require('express');
var http = require('http');

var app = express();
var server = http.createServer(app);

//app.configure, app.use etc

server.listen(1234);

What's the difference?
If I navigate to http://localhost:1234, thus I get the same output.

Answer 1

The second form (creating an HTTP server yourself, instead of having Express create one for you) is useful if you want to reuse the HTTP server, for example to run socket.io within the same HTTP server instance:

var express = require('express');
var app     = express();
var server  = require('http').createServer(app);
var io      = require('socket.io').listen(server);
...
server.listen(1234);

However, app.listen() also returns the HTTP server instance, so with a bit of rewriting you can achieve something similar without creating an HTTP server yourself:

var express   = require('express');
var app       = express();

// app.use/routes/etc...

var server    = app.listen(3033);
var io        = require('socket.io').listen(server);

io.sockets.on('connection', function (socket) {
  ...
});

Answer 2

There is one more difference of using the app and listening to http server is when you want to setup for https server

To setup for https, you need the code below:

var https = require('https');
var server = https.createServer(app).listen(config.port, function() {
    console.log('Https App started');
});

The app from express will return http server only, you cannot set it in express, so you will need to use the https server command

var express = require('express');
var app = express();
app.listen(1234);