Node.js

An Introduction to get you started!

Created by Abdel Raoof Olakara

Agenda

• What is Node.js
• Architecture
• Understanding Concepts
• Programming & Demos

A brief History of Node.js

• Created by Ryan Dahl & published for Linux in 2009
• Later sponsored by Joyent
• Package Manager (NPM) was introduced in 2011
• Native Windows implementation released in June 2011
• io.js a fork of Node.js appears in December 2014
• Node.js Foundation was announced in February 2015
• io.js & Node.js first merged release September 2015
• First LTS (4.2.0) released in October 2015
• Latest release (5.1.0) released in November 2015

Node.js Architecture

V8

V8 is a JavaScript engine written in C++.

• JIT (Just-In-Time) compiler instead of a JavaScript interpreter.
• V8 implements ECMAScript as specified in ECMA-262
• It can run standalone, or can be embedded into any C++ application.
• Implements an efficient Garbage Collection mechanism to reclaim memory

Libuv

libuv is a multi-platform support library with a focus on asynchronous I/O.

• Full-featured event loop backed by epoll, kqueue, IOCP, event ports.
• Asynchronous TCP and UDP sockets
• Asynchronous DNS resolution
• Asynchronous file and file system operations
• File system events
• IPC with socket sharing, using Unix domain sockets or named pipes (Windows)
• Child processes
• Thread pool

Multi threaded HTTP Server

courtesy: Strongloop

Node.Js HTTP Server

courtesy: Strongloop

Node.js Event Loop

Concepts: Modules

• Provides a way to break large JavaScript application into multiple files
• Provides ability to reuse the code, share it etc
• Node.js implements the Common.Js Module pattern
• You can include a module by using 'require'.

  var myModule =  require('module-name');

• You can export functionality using 'exports' in a Module

  exports.variable = variable / function;

Concepts: Modules

How Modules are loaded?

•   Global always overrides the local
•   Looks for module in node_modules folder
•   Traverses up the directory hierarchy
•   Looks for *.js, *.json & *.node

Concepts: Callbacks

function slowAlert() {
  alert("That was really slow!");
}
.
.
.
timeoutID = window.setTimeout(slowAlert, 2000);

- Callback is a parameter to a function that happens to be a function itself!

Concepts: Callbacks

- All APIs of Node are written is such a way that they supports callbacks. - In Node.js a callback function is called at the completion of a given task. - Node.js uses a callback concept called "error-first callbacks".

fs.readFile('input.txt', function (err, data) {
    if (err) return console.error(err);
    console.log(data.toString());
});

Concepts: Events

• Node.js is coded around events
• You start your server, initiate most of the variables, declare your functions and then just wait for an event to occur.
• There are lots of built-in events
• You have the ability to create events using events module

var events = require('events');
var eventEmitter = new events.EventEmitter();

var sayHello = function() {
  console.log('Hello there..');
}

eventEmitter.on('sayHello', sayHello);

eventEmitter.emit('sayHello');

Pros & Cons

Pros of using Node.js

• Fast - Execution Speed
• ALM turnaround is small
• Great Community
• Proven to handle high volume systems
• Most suited for networking applications
• Most suited for I/O intensive applications

Pros & cons

Cons of using Node.js

• Writing event driven code have a learning curve
• Writing huge business centric systems
• Callback hell
• Exception handling is not straight forward

Best Scenarios for using Node.js

• Most suited for networking & I/O intensive applications
• Application that need high concurrency & queued concurrent inputs
• Streaming applications like media streaming, chat applications
• Proxy service
• Real time applications
• Dashboard applications
• Exposing REST APIs

REPL

• REPL - Read, Evaluate, Print, Loop
• It is the Node.js shell
• It provides a way to interactively run JavaScript and see the results
• REPL can be started by simply running node on shell/console without any argument

Demos

- REPL hands on! - Hello World Application - Modules - A Simple Web server

How can we make use of Node.js

• Hosting Static files
• Automation libraries like gulp, grunt, sass or css compilers, bower etc
• Build automation and productivity tools for internal use

THE END

Learn more... - Learn All The Nodes - NodeSchool.io