A Runtime Environment to run JavaScript outside the Browser. Think: Server-side JavaScript interpreter.

It uses Chrome's V8 JavaScript engine to compile JS commands into executable code.

It is a free and open source software created in 2009 by Ryan Dahl.

Details

• It's cross-platform and is mainly used to build backend services (APIs, servers, etc.) and Command line tools.
• Uses the same JavaScript language that the browser uses, but has access to different context and APIs:
  • Browser: document, location, window, accelerometer, geolocation, etc. (Browser APIs)
  • Node: fs (file system), os (operating system), http, etc.
• Node.js has the largest open source library in the world: The NPM.

1) Go to: https://nodejs.org/en/download/

2) Download the LTS version for your platform and follow the instructions

3) Once installed, open the terminal and check that node has been installed:

$ node --version

You should see something like this:

v14.15.4

LTS: Stability, rare updates, enterprise-level apps and services, long-term support: 18 months. Better suited for production.

Current/Stable: Front-end tools, local development, regular updates, new features, performance updates, bug fixes, cutting-edge technologies, etc. Support for approximately 8 months.

If you are ready for production, hit for LTS.
Otherwise use Current.

References:

What is the difference between the LTS version
and the stable version of node.js?

What are the differences between Long Term Support (LTS) and Stable versions of Node.js?

$ mkdir app

$ cd app

$ touch app.js

console.log('Node!');

$ node app.js

$ code app.js

console.log( window );

$ node app.js

 ReferenceError: window is not defined

We are not running JS in the browser where the window global object is available.

Built-in functions such as setTimeout() are available both on Node.JS and the Browser.

On the Browser, these built-in functions are methods of the global window Object, whereas in Node.js they are methods of the global object:

window.setTimeout

global.setTimeout

Open up your terminal and type

$ node

> 4+6

10

Basic REPL commands

> .exit

> .help

> .break or .clear

> .editor

> .save

> .load

> console.clear(); or CTRL+L

Every file in Node is considered a Module.

console.log( module ); 
// NOT a global.module object!

Module {
    ...
    exports: {},
    ...
}

Module global variables available: exports, require, module, __filename, __dirname

Think of each JavaScript file a separate Module with its own private scope and context.

$ touch app.js 

console.log( module ); 

$ node app.js 

*The touch command creates a new file in *nix systems

1) Your own source files

2) Core node modules

3) Installed dependencies in node_modules/ folder

$ touch logger.js

let message = "Module";

function log(){ 
    console.log( message );
}

module.exports = log;

Both log and message are scoped into the module and are not available outside the module (file). We try to export only a minimal amount of variables and keep things private in the Module.

We can also export multiple values:

module.exports.log = log;

app.js:

const logger = require( './logger.js' );
// We must be on the same folder here
console.log( logger );
logger();   // Custom variable name here

We could have used:

require( './folder/logger.js' );

or:

require( '../logger.js' );

BEST PRACTICE: use a const to store require() objects.

app.js:

const fs = require( 'fs' );
const files = fs.readdirSync( './' );

files will be a String Array

console.log( files );

app.js:

const fs = require( 'fs' );
const files = fs.readdir( './', ( err,files )=>{

    if ( err ) {
        console.log( err );
    } else {
        console.log( files );
    }

}); 

BEST PRACTICES: Prefer asynchronous methods instead of sync (readdirSync) for non-blocking code.

*Add 2 console.log statements to test asynchronous code

app.js:

const fs = require( 'fs' );
let contents = fs.readFileSync( 'app.js' );
console.log( contents );

What do you see in the console?

Let's try again with one small addition...

contents = fs.readFileSync( 'app.js','utf8' );
console.log( contents );

*Add some error handling using try { } catch { }

app.js:

const fs = require( 'fs' );
fs.readFile( 'app.js', ( err, buffer )=>{
    console.log( buffer.toString() );
});

app.js:

const fs = require( 'fs' );

// SYNC:
fs.writeFileSync( 'test.txt', "TEXT DATA" );

// ASYNC:
fs.writeFile( 'test.txt', "TEXT DATA",  ( err )=>{
    if ( err ){
        console.log( err.message );
    }
});

app.js:

const path = require('path'); 
let pathObj = path.parse(__filename);

__filename: The file name of the current module.

{ 
    root: '/',
    dir: '/Users/kostasx/Desktop',
    base: 'app.js',
    ext: '.js',
    name: 'app' 
}

app.js:

const path = require('path'); 
let arguments = process.argv;
// process.argv == Array of command line arguments
let pathObj = path.parse( arguments[2] );
console.log( pathObj );

process: global object that provides information about, and control over, the current Node.js process. It is always available to Node.js apps without require();

app.js:

const os = require('os');

os.totalmem();
os.freemem(); 

console.log( `Total Memory: ${os.totalmem()}` );

Google for: js convert bytes to gb
refactor code to display the total memory in GB

The official package manager for Node and is bundled & installed automatically with the environment.

$ npm --version

• npm install package-name
  const package = require('package-name');
• npm init
  npm init -y
  package.json
• npm install package-name --save
  npm install package-name --save-dev
• .gitignore

A file that serves as documentation
for what packages your project depends on.

Allows you to specify the versions of a package that your project can use using semantic versioning rules.

$ npm install lodash@4.17.4

Makes your build reproducible which means that its way easier to share with other developers.

Pluralize

$ npm install pluralize --save

const pluralize = require('pluralize');

let result = pluralize('test');
console.log( "test: ", result );

result = pluralize('paper');
console.log( "paper: ", result );

result = pluralize('mummy');
console.log( "mummy: ", result );

Colors

$ npm install colors --save

require('colors');

console.log('hello'.green); // outputs green text
console.log('i like cake and pies'.underline.red) // outputs red underlined text
console.log('inverse the color'.inverse); // inverses the color
console.log('OMG Rainbows!'.rainbow); // rainbow

Convert-Units

$ npm install convert-units --save

const convert = require('convert-units');

// Days to Hours
let result = convert(1).from('d').to('h');
console.log( result );

// Week(s) to Days
result = convert(1).from('week').to('d');
console.log( result );

// Kilobytes to MBytes
result = convert(1024).from('Kb').to('Mb');
console.log( result );

Putting it all together

require('colors');
const pluralize = require('pluralize');
const convert = require('convert-units');

let MB = convert(1024).from('Kb').to('Mb');
let output = MB + " " + pluralize('megabyte', MB);

console.log( output.red );

// Parse URLs
const url = require('url'); 

// Lets Pluralize!
const pluralize = require('pluralize');

You will need npm install pluralize for the 2nd module...