A introduction to NODEJS

1. ndjidoardo.bar@hypercube-research.com

2.  JavaScript created in 1995 by Brendan Eich (@Netscape labs) .
 JS become a ECMA (European Computer Manufacturers
Association) standard by 1997. It remains a standard in client-
side app over years.
 Google V8, chrome, Sep 2008
 Node created in 2009 by Ryan Dahl using V8 power (c++ &
javascript) : With Node JS start being as a server-side language.

3.  Highly scalable web servers for web applications.
 Web services (RESTful API)
 Real-Time apps as its supports Web-Sockets.
 App with queued inputs.
 Data streaming apps.

5.  Single-threaded execution with the use of callback functions => not resource-
intensive
◦ suitable for high latency I/O operations e.g: database access
◦ Scalable as it combines Server and application logic in one single place

6.  Node is event-driven, it handles all requests asynchronously from on single
thread.
 A event loop is used to schedule tasks in the event-driven programming.
 Node programming style is christened Continous-Passing Style (CPS): Every
asynchronous function has at least a Callback function as one of its parameters.
This later is call after the asynchronous section is executed.
var fs = require("fs");
fs.readFile ("foo.txt", "utf8", function(error,
data) {
if (error) {
throw error;
}
console.log(data);
});
console.log("Reading file...");

7.  Using async module
 Using process.nextTick() trick:
function add (x, y, callback) {
setTimeout(function() {
callback(x + y);
},0);
}
add(2, 3, console.log);
console.log("The sum is:" );
function add (x, y, callback) {
process.nextTick(function() {
callback(x + y);
});
}
add(2, 3, console.log);
console.log("The sum is:" );

8.  Non-blocking has always to do with I/O (file system,
database,…)
 The following code is asyn but not Non-blocking:
function add (x, y, callback) {
process.nextTick(function() {
while (1) {
callback(x + y);
}
});
}
add(2, 3, console.log);
console.log("The sum is:" );

9.  Install NodeJS :
http://nodejs.org/download/

10.  Create a app.js file with the following code:
 Start your server by issuing the following cmd:
◦ > node app.js
Nb: NodeJS has got a REPL!

11.  NodeJS extensions are known as modules
 NodeJS is being backed by an active community which provides
an overwhelming number of modules
 NPM command is used to install and manage new modules:
◦ Ex:
 npm install async
 npm install async@1.0.x
 npm install –g async
 npm serach <MODULE_NAME>
 npm outdated
 npm update npm –g
 npm rm asyn
 « require(<MODULE_NAME>)» is used to load a given module

12.  ExpressJS helps to fit web projects to MCV design pattern
 To install ExpressJS:
◦ > npm install –g express
 Express has got a scafolding capability that help you create a sustainable
project structure, easy to extend and maintain. Express-generator is the
module dedicated to that job.
◦ > npm install –g express-generator

13.  Find a ExpressJS app example on my GITHUB:
◦ https://github.com/ndjido/NodeJS_intro