Node.js essentials

node essentials.js
Made with by @elacheche_bedis

About me
Bedis ElAcheche (@elacheche_bedis)
- Lazy web & mobile developer
- Official Ubuntu Member
- FOSS lover
- Javascript fanatic
- I’m writing bugs into apps since 2008

What to expect ahead..
- Data types
- Variables
- Conditional statements
- Loops
- Functions
- Comments

What to expect ahead (for real)...
- Introduction
- Event loops
- Blocking and nonblocking I/O
- Modules
- NPM
- Demos
- Random memes

What is Node.js?
- Open source, cross platform development platform.
- A command line tool.
- Created by Ryan Dahl in 2009.
- Uses v8 JavaScript engine.
- Uses an event-driven, non-blocking I/O model.

Why Node.js?
- Free
- Open source
- Very lightweight and fast because it's mostly C/C++ code.
- Can handle thousands of concurrent connections with minimal overhead
(CPU/Memory).
- There are lots of modules available for free.

When to use Node.js?
- HTTP servers.
- Chat applications.
- Online games.
- Collaboration tools.
- Desktop applications.
- If you are great at writing javascript code.

When not to use Node.js?
- Heavy and CPU intensive calculations on server side.
- Node.js is single thread
- You have to write logic by your own to utilize multi core processor and make it
multi threaded.

Who uses Node.js?
- LinkedIn
- Microsoft
- Netflix
- PayPal
- SAP
- Walmart
- Uber
- ...

Event loops
- The core of event-driven programming.
- Almost all the UI programs use event loops to track the user event.
- Register callbacks for events.
- Your callback is eventually red.ﬁ

Event loops
$('a').click(function() {
console.log('clicked!');
});
$.get('slides.php', {
from: 1,
to: 5
}, function(data) {
console.log('New slides!');
});

Event loops life cycle
Event loop
(single thread)
Register callback
Trigger callback Operation
complete
Requests
File System
Database
Network

Event loops life cycle
- Initialize empty event loop.
- Execute non-I/O code.
- Add every I/O call to the event loop.
- End of source code reached.
- Event loop starts iterating over a list of events and callbacks.
- Perform I/O using non-blocking kernel facilities.
- Event loop goes to sleep.
- Kernel noti es the event loop.ﬁ
- Event loop executes and removes a callback.
- Program exits when event loop is empty.

Blocking and nonblocking I/O
// Blocking I/O
var attendees = db.query('SELECT * FROM attendees'); // Wait for result!
attendees.each(function(attendee) {
var attendeeName = attendee.getName(); // Wait for result!
sayHello(attendeeName); // Wait
});
startWorkshop(); // Execution is blocked!

Blocking and nonblocking I/O
// Nonblocking I/O
db.query('SELECT * FROM attendees', function(attendees) {
attendees.each(function(attendee) {
attendee.getName(function(attendeeName) {
sayHello(attendeeName);
});
});
});
startWorkshop(); // Executes without any delay!

Events in Node.js
- An action detected by the program that may be handled by the program.
- Determine which function will be called next.
- Many objects in node emit events.
- You can create objects that emit events too.

Events in Node.js
// Custom event emitters
var EventEmitter = require('events');
var logger = new EventEmitter();
logger.on('new-attendee', function(message) {
console.log('Welcome %s! Please have a seat.', message);
});
logger.on('attendee-left', function(message) {
console.log('Goodbye %s! See you next time.', message);
});
logger.emit('new-attendee', 'John Doe');
// Welcome John Doe! Please have a seat.
logger.emit('new-attendee', 'Jane Doe');
// Welcome Jane Doe! Please have a seat.
logger.emit('attendee-left', 'John Smith');
// Goodbye John Smith! See you next time.

Node.js modules
- External libraries.
- One kind of package which can be published to NPM.
- Node.js heavily relies on modules.
- Creating a module is easy, just put your javascript code in a separate js file
and include it in your code by using keyword require.

Node.js modules
/* Hello world */
var aModule = require('module1');
var otherModule = require('module2');
/* Awesome code */
/* Cool stuff */
app.js
./node_modules
module1.js module2.js

Node.js modules
// greetings.js
var hello = function() {
console.log('Hello %s!', name || '');
}
var bye = function() {
console.log('Bye %s!', name || '');
}
module.exports = {
hello: hello,
bye: bye
};
// hola.js
module.exports = function(name) {
console.log('Hola %s!', name || '');
};
// app.js
var greetings = require('./greetings');
var hola = require('./hola');
greetings.hello();
// Hello!
hola('John doe');
// Hola Jane doe!
// If we only need to call once
require('./greetings').bye('Jane');
// Goodbye Jane!

Node.js modules
How does require return the libraries?// look in same directory
var awesomeModule = require('./awesome-module')
// look in parent directory
var awesomeModule = require('../awesome-module')
// look in specific directory
var awesomeModule = require('/home/d4rk-5c0rp/lab/awesome-module');
// app.js located under /home/d4rk-5c0rp/lab/nodeWorkshop
var awesomeModule = require('awesome-module');
// search in node_modules directories
// /home/d4rk-5c0rp/lab/nodeWorkshop/node_modules
// /home/d4rk-5c0rp/lab/node_modules
// /home/d4rk-5c0rp/node_modules
// /home/node_modules
// /node_modules

NPM
- Package manager for node.
- Comes bundled with Node.js installation.
- Command line client that interacts with a remote registry.
- Allows users to consume and distribute JavaScript modules.
- Manage packages that are local dependencies of a particular project.
- Manage as well globally-installed JavaScript tools.

NPM registry
- Kind of an App store for developers.
- There are a whole lot of modules and tools available to make the process of
building programs quicker and simpler.
- Look up the functionality you want, and hopefully found a module that does it
for you.

Installing a NPM module
npm install
npm install <tarball file>
npm install <tarball url>
npm install <name>
npm install <name>@<tag>
npm install <name>@<version>
npm install <name> [--save|--save-dev]
Install modules into local node_modules directory
If a module requires another module to operate, NPM will download
automatically!

Installing a NPM module
npm install gulp -g
Install modules with executables globally
Global NPM modules CAN’T be required
var gulp = require('gulp');
// Error: Cannot find module 'gulp'

Express.js
- Minimal and flexible Node.js framework.
- Free and open-source.
- Designed for building web applications and APIs.

Socket.IO
- Realtime application framework.
- Enables bidirectional event-based communication.
- It has two parts: a client-side library that runs in the browser, and a server-side
library for Node.js.

slides.emit('Thank you!');
Made with by @elacheche_bedis

Node.js essentials

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