NODE.JS ARCHITECTURE AND
GETTING STARTED WITH EXPRESS.JS
Jordan Kasper | Developer Evangelist

NODE.JS ARCHITECTURE

MODULARITY

MODULE PATTERNS
There are various patterns...
Simple Object API
Revealing Module (Function Initialization)
Object Constructor

SIMPLE OBJECT API
// lib/employee.js
module.exports = {
salary: 50000,
giveRaise: function( amount ) {
salary += amount;
}
};
Why not always use simple objects?
Modules are cached!

REVEALING MODULE PATTERN
module.exports = function createWorker( options ) {
// Setup...
return {
salary: 50000,
giveRaise: function( amount ) {
this.salary += amount;
}
};
};

OBJECT CONSTRUCTOR PATTERN
var Worker = module.exports = function Worker( options ) {
// ...
};
Worker.prototype.salary = 50000;
Worker.prototype.giveRaise = function( amount ) {
this.salary += amount;
};

SCALING

VERTICAL SCALING

NODE CLUSTERING

var http = require('http'),
cluster = require('cluster');
if (cluster.isMaster) {
for (var i = 0; i < numCPUCores; i++) {
cluster.fork();
};
} else {
http
.createServer(function(req, res) {
// ...
})
.listen(8080, ...);
});

USING A PROCESS MANAGER
Easy clustering and scaling without altering application
code
StrongLoop Process Manager (strong-pm)
PM2
Comparison Chart
Forever

LOAD BALANCING
cluster uses a simple round-robin approach...
...but there are better ways!

HORIZONTAL SCALING

HORIZONTAL SCALING

Nginx

BASIC NGINX CONFIG
server {
listen 80
location / {
proxy_pass http://localhost:3000;
}
location /static/ {
root /var/www/my­app/public;
}
}
$ sudo service nginx start

NGINX LOAD BALANCER
http {
upstream myapp {
least_conn; # round­robin is the default...
# Or use ip_hash; for "sticky" sessions...
server www1.my­app.com;
server www2.my­app.com;
server www3.my­app.com;
}
server {
listen 80
location / {
proxy_pass http://myapp;
}
}
}

STRONGLOOP AND NGINX
If you're using strong-pm you can use the
!
StrongLoop nginx
controller
~$ npm install ­g strong­nginx­controller
~$ sl­nginx­ctl­install
Install the Controller on the load balancing host...

...then manage the load balancing infrastructure from
:StrongLoop Arc

SCALING WITH STRONGLOOP ARC

Nginx

EXPRESS.JS

EXPRESS.JS
Fast, light, unopinionated framework for web applications.

EXPRESS HELLO WORLD
~/my­app$ npm init
...
~/my­app$ npm install express ­­save

EXPRESS HELLO WORLD
// in app.js
var express = require('express');
var myApp = express();
myApp.get('/', function handleRoot(req, res, next) {
res.send('Hello World!');
});
myApp.listen(8080);
~/my­app$ node app.js

SCAFFOLDING AN EXPRESS APP

SCAFFOLDING EXPRESS
Install the CLI generator first...
~$ npm install ­g express­generator
~$ express my­app
...
~$ cd my­app
~/my­app$ npm install

A SCAFFOLDED APP
my­app/
|_ bin # execution file (shell script)
|_ node_modules
|_ public # images, css, fonts, etc
|_ routes # Node.js routing code
|_ views # server­side templates
|_ app.js
|_ package.json

RUNNING A SCAFFOLDED APP
~/my­app$ npm start
{
...,
"scripts": {
"start": "node ./bin/www"
},
...

CONFIGURING EXPRESS

CONFIGURING EXPRESS
var app = express();
app.set('views', 'views');
app.set('view engine', 'jade');
app.set('port', process.env.PORT || 3000);
app.set('foo', 'bar');
server.listen( app.get('port') );

REQUEST ROUTING

BASIC ROUTING
var express = require('express');
var myApp = express();
myApp.get('/', function handleRoot(req, res, next) {
res.send('Hello World!');
});
myApp.listen( 3000 );

POST ROUTING
myApp.post('/user', function createUser(req, res, next) {
// Create the user record...
res.redirect('/my­account');
});

POST ROUTING
myApp.post('/user', function createUser(req, res, next) {
// Create the user record...
// Where do we get the data from?
res.redirect('/my­account');
});

MIDDLEWARE

MIDDLEWARE EXAMPLES
var express = require('express'),
bodyParser = require('body­parser');
var app = express();
// app config...
// Parse POST form data...
app.use( bodyParser.urlencoded({ extended: false }) );
app.post('/user', function createUser() {
var user = {
username: req.body.username,
...
};
...
});

ORDER MATTERS!
Middleware are executed in the order specified
app.use( express.logger('dev') );
app.use( myAuthModule() );
app.use( bodyParser.json() );
app.use(bodyParser.urlencoded({ extended: false }));
app.use(express.static(path.join(__dirname, 'public')));
// Routing middleware...

MIDDLEWARE - WHEN DOES IT END?
Middleware processing ends when next() is not called
(or an error is generated)
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.get('/about', function aboutUs(req, res, next) {
res.send('We are StrongLoop!');
// no call to next()
});
app.get('/user', ...);

CUSTOM MIDDLEWARE
app.use(function (req, res, next) {
// Do some work...
// Modify the req or res...
// execute the callback when done
next();
});

CUSTOM MIDDLEWARE - ERRORS
app.use(function (req, res, next) {
// do something...
if (thereWasAnError) {
var err = new Error(' ... ');
next( err );
return;
}
// No error, so we proceed...
next();
});

HANDLING MIDDLEWARE ERRORS
app.use(function(err, req, res, next) {
// Do whatever you need to...
if (err.code === 404) {
res.redirect('/error­404');
} else {
// Or you can keep processing this (or a new) Error
next(err);
}
});

HANDLING MIDDLEWARE ERRORS
Always set up a "catchall" error handler!

SERVER-SIDE TEMPLATING

TEMPLATES
Small blocks that we can plug data into at run-time
//­ /views/index.jade
doctype html
html
head
title #{title}
body
section.main­body.clear
#{homepageText}

TEMPLATING ENGINE
~/my­app$ npm install ­­save jade
var app = express();
app.set('views', 'views');
app.set('view engine', 'jade');

USING A TEMPLATE
app.get('/' function handleRoot(req, res, next) {
res.render('index', {
title: 'StrongLoop ­ Home',
homepageText: 'We all love StrongLoop!'
});
});

DON'T FORGET YOUR MODULARITY!

NOT MODULAR...
var express = require('express'),
bodyParser = require('body­parser');
var app = express();
// app config and other middleware...
app.post('/user', function createUser() {
var user = {
username: req.body.username,
...
};
db.create(user, function() {
res.render('user/my­account', { ... });
});
});

THE 4.0 ROUTER INTERFACE
// in routes/users.js
var express = require('express');
var router = express.Router();
router.get('/', function(req, res, next) {
// Get a list of users...
res.render('user/list', { results: users });
});
router.get('/:id', function(req, res, next) {
// Get a single user...
res.render('user/my­account', { user: user });
});
router.post('/', function(req, res, next) {
// Create a user...
res.redirect('user/my­account', { user: user });
});
module.exports = router;

THE 4.0 ROUTER INTERFACE
// in app.js
var express = require('express'),
...;
var app = express();
// app config and middleware...
app.use('/users', require('./routes/users'));

REQUEST OBJECT

QUERY PARAMETERS
app.get('/users', function (req, res, next) {
var limit = req.query.limit || 10,
users = [];
// Retrieve all users...
res.render('user/list', {
results: users,
nextIndex: 11
});
});

URL PARAMETERS
app.get('/users/:id', function (req, res, next) {
var id = req.params.id,
user = null;
// Retrieve a single user...
if (req.xhr) {
res.json({ user: user });
} else {
res.render('user/single', {
user: user
});
}
});

URL PARAMETERS
app.get(/^/users/(d+)$/, function (req, res, next) {
var id = req.params[0],
user = null;
// Retrieve a single user...
// ...
});

RESPONSE OBJECT

RESPONSE METHODS
response.send(data) or response.end(data)
response.status(httpStatus)
response.send(201, someData)
response.sendfile('path/to/someFile.json')
response.download('/report-12345.pdf')

HTTP STATUS CODES
2XX: for successfully processed requests
3XX: for redirections or cache information
4XX: for client-side errors
5XX: for server-side errors

QUESTIONS?
NODE.JS ARCHITECTURE AND
GETTING STARTED WITH EXPRESS.JS
Jordan Kasper | Developer Evangelist
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