Run through of setting up a basic node app with express

## app.js
var express = require('express');

// Middleware to parse body of HTTP requests
var bodyParser = require('body-parser');

// Invokes function returned from require.
// Creates an Express application;
// express() returns Express object
var app = express();

// Sets port equal to either the environment
// PORT variable OR 3000 as default.
// Can set up environment variables on servers
// when deploying for production.
var port = process.env.PORT || 3000;

// Create parser for requests with
// Content-Type: x-www-form-urlencoded
var urlencodedParser = bodyParser.urlencoded({ extended: false });

// Create parser for requests with
// Content-Type: application/json
var jsonParser = bodyParser.json();

// Mounts specified middleware function(s) at specified path;
// app.use() takes following params:
// 1. path: string|RegExp | (string|RegExp)[]
// 2. ...handlers: RequestHandler[] (callback functions, can be series of functions
// separated by commas or array of functions)
// Middleware function is executed when the base of
// the requested path matches path param.
// express.static() is built-in express middleware
// to serve static files.
// express.static() takes following params:
// 1. root: string (dir from which static assets to be served)
// 2. options?: serveStatic.ServeStaticOptions
// Here we have a 'public' folder in root dir with a style.css file
app.use('/assets', express.static(__dirname + '/public'));

// Make your own middleware.
app.use('/', function(req, res, next){
    console.log('Request Url: ' + req.url);
    // Express provides next() for middleware to the
    // function that you give as callback when route is matched.
    // next() just means 'run the next middleware';
    // Without next(), request will be left hanging.
    next();
});

// Executes this function if a GET request
// is received to this url.
app.get('/', function(req, res) {
    // Indicate body to be included in response.
    // Don't need to indicate Content-type header.
    // When browser sees href=assets/style.css it will
    // generate an HTTP req for site/assets/style.css,
    // and this will be handled by Node.
    // When it sees /assets it will handle request in
    // app.use('/assets' ...).
    res.send('<html><head><link href=assets/style.css type=text/css rel=stylesheet /></head><body><h1>Donuts</h1></body></html>');
});

// Use res.sendFile to serve an html file
app.get('/form', function(req, res){
    res.sendFile(__dirname + '/form.htm');
});

// :id indicates that id is a variable name.
// Access id using req.params.id.
// Can also access request query string using req.query.param,
// where param is name from a query string name value pair
// (ie url?param=4&name=value).
// Now we can access urls such as:
// /person/3
// /person/Jerry
app.get('/person/:id', function(req, res) {
    res.send('<html><head></head><body><h1>Donuts for Person ' + req.params.id + '</h1></body></html>');
});

// Pass urlencodedParser (middleware we created earlier)
// to post statement as a callback.
// urlencodedParser is middleware that will be called
// before function(req, res) is called.
// urlencodedParser gives us access to req.body.param,
// where param is name of name value pair in body of request.
// So if '/person' is seen in the url, and it's of method post,
// then this middleware and callback will be run.
app.post('/person', urlencodedParser, function(req, res){
    res.send('Thank you!');
    console.log(req.body.firstname);
    console.log(req.body.lastname);
});

// Pass jsonParser (middleware we created earlier)
// to post statement as a callback.
// jsonParser gives us access to req.body.param,
// where param is name in json object in body of request.
app.post('/personjson', jsonParser, function(req, res){
    res.send('Thankyou for the json data');
    console.log(req.body.firstname);
    console.log(req.body.lastname);
});

// Send json data in response to GET from /api url
app.get('/api', function(req, res) {
    res.json({ firstname: 'Jelly', lastname: 'Donut' });
});

// listen() calls http.createServer under the hood.
// listen() takes the following params:
// 1. port: number
// 2. hostname: string
// 3. backlog: number
// 4. callback?: Function
// returns a http.Server object.
// Here we specify port 3000.
app.listen(port);
	var express = require('express');

	// Middleware to parse body of HTTP requests
	var bodyParser = require('body-parser');

	// Invokes function returned from require.
	// Creates an Express application;
	// express() returns Express object
	var app = express();

	// Sets port equal to either the environment
	// PORT variable OR 3000 as default.
	// Can set up environment variables on servers
	// when deploying for production.
	var port = process.env.PORT \|\| 3000;

	// Create parser for requests with
	// Content-Type: x-www-form-urlencoded
	var urlencodedParser = bodyParser.urlencoded({ extended: false });

	// Create parser for requests with
	// Content-Type: application/json
	var jsonParser = bodyParser.json();

	// Mounts specified middleware function(s) at specified path;
	// app.use() takes following params:
	// 1. path: string\|RegExp \| (string\|RegExp)[]
	// 2. ...handlers: RequestHandler[] (callback functions, can be series of functions
	// separated by commas or array of functions)
	// Middleware function is executed when the base of
	// the requested path matches path param.
	// express.static() is built-in express middleware
	// to serve static files.
	// express.static() takes following params:
	// 1. root: string (dir from which static assets to be served)
	// 2. options?: serveStatic.ServeStaticOptions
	// Here we have a 'public' folder in root dir with a style.css file
	app.use('/assets', express.static(__dirname + '/public'));

	// Make your own middleware.
	app.use('/', function(req, res, next){
	console.log('Request Url: ' + req.url);
	// Express provides next() for middleware to the
	// function that you give as callback when route is matched.
	// next() just means 'run the next middleware';
	// Without next(), request will be left hanging.
	next();
	});

	// Executes this function if a GET request
	// is received to this url.
	app.get('/', function(req, res) {
	// Indicate body to be included in response.
	// Don't need to indicate Content-type header.
	// When browser sees href=assets/style.css it will
	// generate an HTTP req for site/assets/style.css,
	// and this will be handled by Node.
	// When it sees /assets it will handle request in
	// app.use('/assets' ...).
	res.send('<html><head><link href=assets/style.css type=text/css rel=stylesheet /></head><body><h1>Donuts</h1></body></html>');
	});

	// Use res.sendFile to serve an html file
	app.get('/form', function(req, res){
	res.sendFile(__dirname + '/form.htm');
	});

	// :id indicates that id is a variable name.
	// Access id using req.params.id.
	// Can also access request query string using req.query.param,
	// where param is name from a query string name value pair
	// (ie url?param=4&name=value).
	// Now we can access urls such as:
	// /person/3
	// /person/Jerry
	app.get('/person/:id', function(req, res) {
	res.send('<html><head></head><body><h1>Donuts for Person ' + req.params.id + '</h1></body></html>');
	});

	// Pass urlencodedParser (middleware we created earlier)
	// to post statement as a callback.
	// urlencodedParser is middleware that will be called
	// before function(req, res) is called.
	// urlencodedParser gives us access to req.body.param,
	// where param is name of name value pair in body of request.
	// So if '/person' is seen in the url, and it's of method post,
	// then this middleware and callback will be run.
	app.post('/person', urlencodedParser, function(req, res){
	res.send('Thank you!');
	console.log(req.body.firstname);
	console.log(req.body.lastname);
	});

	// Pass jsonParser (middleware we created earlier)
	// to post statement as a callback.
	// jsonParser gives us access to req.body.param,
	// where param is name in json object in body of request.
	app.post('/personjson', jsonParser, function(req, res){
	res.send('Thankyou for the json data');
	console.log(req.body.firstname);
	console.log(req.body.lastname);
	});

	// Send json data in response to GET from /api url
	app.get('/api', function(req, res) {
	res.json({ firstname: 'Jelly', lastname: 'Donut' });
	});

	// listen() calls http.createServer under the hood.
	// listen() takes the following params:
	// 1. port: number
	// 2. hostname: string
	// 3. backlog: number
	// 4. callback?: Function
	// returns a http.Server object.
	// Here we specify port 3000.
	app.listen(port);