• Node JS
  • Topics
  • What is node js
  • Prerequisites
  • Why use node?
  • Real time used of Nodejs
  • NPM
  • Node Modules
  • Initialize package.json
  • Installing Packages
  • Using Node.js
  • Exporting Modules
  • Directory
    • ECMAScript Module
  • Code Modules
  • Path modules
  • File System (fs) module

As an asynchronous event-driven JavaScript runtime, Node.js is designed to build scalable network applications. https://nodejs.org/en/about

1. JavaScript Runtime (NOT a language or a framework)
2. Built on the V8 JavaScript engine (Same a Google Chrome)
3. Written in C++
4. Essentially allows us to run JavaScript code on the server

• JavaScript Fundamentals (Objects, Arrays, Conditionals, etc)
• HTTP (status codes, headers, etc)
• JSON
• Arrow Functions
• Promises
• MVC Pattern

1. Fast, efficient and highly sclabale
2. Event driven, non-blocking I/O asynchronous model
   • Non-blocking Input/Output:
     • Allows code to continue running while waiting for tasks like reading files or making network requests.
     • Increases efficiency by not blocking the entire program during I/O operations.
   • Single-threaded Event Loop:
     • Node.js uses a single thread to handle multiple tasks.
     • The event loop manages asynchronous operations, enabling efficient handling of concurrent tasks without blocking the program.
     • Supports concurrency via events & callbacks
     • EventEmitter class is used to bind events and listeners
3. Popular in the industry
4. Same language on the front and back end (JS)

• REST API & Microservices
• Real Time Services (Chat, Live Updates)
• CRUD Apps - Blogs, Shopping Carts, Social Networks
• Tools & Utilities

Short Answer: Anything that is not CPU intensive, means I/O operations are asynchronous, these things CPU intensive making request to server. sending data to a server. getting response from a server. CPU calculations.

Node Package Manager

• Install 3rd party packages (frameworks, libraries, tools, etc)

• Packages get stored in the "node_modules" folder

• All dependencies are listed in a "package.json" file

• NPM scripts can be created to run certain tasks such as run a server

• npm init               Generates a package.json file

• npm install express        Installs a package locally

• nom install -g nodemon   Installs a package globally

• Node Core Modules (path, fs, http, etc)
• 3rd party modules/packages installed via NPM
• Custom modules (files)

const path = require ('path');
const myFile = require ('./myFile');

$ npm init # initializing the package.json
# Provide details

Then it shows on screen a utility will walk you through creating a package.json file. Type the information based on it ask.

{
  "name": "hello-world",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Salman",
  "license": "ISC"
}

Search in NPM - Node Package Manager website as sillyname. A random name generator.

$ npm install 'package-name'

$ npm install uuid # It will install the Unique Random Id generator package in that folder

$ npm install --save-dev nodemon # It will install nodemon package as Developer dependency package.
$ npm install -D nodemon  # short hand 

$ npm i sillyname # short hand `i` for `install`

From website copy the two lines of code and paste into index.js

var generateName = require('sillyname');
var sillyName = generateName();

console.log(`My name is ${sillyName}.`); // My name is 'Joker'
// Run index.js in terminal `node index.js`

Node Read Eval Print Loop (Node REPL) is a computer environment where user inputs are read and evaluated, and then the results are returned to the user.

In terminal, just type node and hit enter.

$ node

You will see the welcome note(you are in REPL environment)and right hand arrow > and type .help, to know about REPL.

ctrl + c to exit the REPL environment

create a index.js file in any folder like (Node folder), write a code console.log("Hello world!") and then open terminal type node index.js. You will see the output as Hello world!.

In Node.js, module.exports is a special object that is used to define what a module exports and makes it available for other modules to require.

//  Basic Exporting and requiring/Importing modules
// person.js
const person = {
  name: 'Salman',
  age: 25,
}
module.exports = Person;

// Index.js
const person = require('./person');
console.log(person); // output:  { name: 'Salman', age: 25, }


// Class level
// Person.js
class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  greeting() {
    console.log(`My name is ${this.name} and I am ${this.age}`);
  }
}
module.exports = Person;

// Index.js
const Person = require('./Person');
const person1 = new Person('Salman', 25);
person1.greeting(); // output:  My name is Salman and I am 25

__dirname and __filename are special variables that provide information about the current directory and filename of the module, respectively.

console.log(__dirname)    // /path/to/your/project/
console.log(__filename)   // /path/to/your/project/index.js

To use ESM, we have to add dependencies in package.json file as "type":"module",.

{
  "name": "hello-world",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
+ "type":"module",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Salman",
  "license": "ISC"
}

ESM is new module. Default type is CJS

1. CJS

var pack = require('<packageName>');

var pack = require('sillyname');

2. ESM

import pack from "<packageName>";

import pack from "sillyname";

Node Code Modules

// path_demo.js
const path = require('path');

// Base file name
console.log(path.basename(__filename));   // path_demo.js

// Directory name
console.log(path.dirname(__filename));    // usr/desktop/node/demo

// File extension
console.log(path.extname(__filename));    // .js

// Create path object
console.log(path.parse(__filename));
/*
{ root: "/",
  dir: '/Users/bradtraversy/node_crash_course/reference',
  base: 'path_demo. js'
  ext: ' js',
  name: 'path demo'
}
*/

// Create path object
console.log(path.parse(__filename).base);                 // path_demo.js

// Concatenate paths
console.log(path.join(__dirname, 'test', 'hello.html'));  // usr/desktop/node/demo/test/hello.html

Link to the Docs

const fs = require('fs');
const path = require('path');

the fs.readFileSync() method, we can synchronously read files, i.e. we are telling node.js to block other parallel processes and do the current file reading process.

2M-Edical