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Node JS

Updated
17 Sept 2026
4 min read
5 sections
Page 2 of 5
MERN Stack Tutorial

Node JS

  • Node JS Installer
  • Node JS Documentation
  • npm init command is used to initial a package.json file.
  • node <filename>.js command is used to run a javascript file using NodeJS
  • To use NodeJS in web browser, in index.html add <script src=""></script>
html
  <!DOCTYPE html>
  <html lang="en">
    <head>
      <meta charset="UTF-8" />
      <meta
        name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"
      />
      <meta http-equiv="X-UA-Compatible" content="ie=edge" />
      <title>Document</title>
    </head>
    <body>
      <script src="./index.js"></script>
    </body>
  </html>

Node Modules

  1. File Based
  2. Build In
  3. Third Party

1. File Based

index.js file

  • module.exports = {a, b} is used to export the selected modules, for re-use of code.
javascript
// console.log("Hello World")

const a = 100;

const b = {
  average: (a, b) => {
    console.log((a + b) / 2);
  },
  percent: (a, b) => {
    console.log(a / b / 100);
  },
};

module.exports = { a, b };

app.js file

  • require() is a built-in function to include external modules that exist in separate files
javascript
const { a, b } = require("./index.js");

console.log(a);

b.average(10, 20);
b.percent(10, 20);

2. Build In

  • fs (File System Module) allows us to work with files present locally in the system.
  • path module allows us to work with directories and file paths.
  • os (Operation System module) provides information about the computer's operating system.
  • events helps trigger an action / event on a computer

Reading Files

  • reading value from sample.txt file
text
  Hello NodeJS !

Asynchronous Functions

  • The heavy tasks are worked in background meanwhile, rest of the code is executed once
  • heavy task is executed the Call-Back function is called Non-Blocking Nature ✅
  • asynchronouse.js file
javascript
  const fs = require("fs");

  // console.log(fs);

  fs.readFile("./sample.txt", "utf-8", (error, data) => {
    if (error) {
      throw error;
    }
    console.log(data);
  });

  console.log("I am First");
  • Output
shell
  I am First
  Hello NodeJS !

  Process finished with exit code 0
  • console.log("I am First") is executed first because fs.readFile() is Asynchronous function

Synchronous Function

  • Runs file line by line, waits of complete execution current line complete
  • Makes JavaScript Code Slow and is called Blocking Nature ❌
  • synchronous.js file
javascript
  const fs = require("fs");

  const a = fs.readFileSync("./sample.txt", "utf-8");

  console.log(a);
  console.log("I am first");
  • Output
shell
  Hello NodeJS !
  I am first

  Process finished with exit code 0

Writing Files

Asynchronous Function

  • asynchronous.js file
javascript
  const fs = require("fs");

  const a = "This is output";

  fs.writeFile("./sample.txt", a, () => {
    console.log("Written");
  });

  console.log("I am First");
  • Output
shell
  I am First
  Written

  Process finished with exit code 0
  • sample.txt file
text
  This is output

Synchronous Function

  • synchronous.js file
javascript
  const fs = require("fs");

  const a = "This is output";

  fs.writeFileSync("./sample.txt", a);

  console.log("Written");
  console.log("I am First");
  • Output
shell
  Written
  I am First

  Process finished with exit code 0
  • sample.txt file
text
  This is output

3. Third Party

  • Third Party modules are modules which are written by some else, and are used in a project.
  • Examples: Express, Gulp, React, Mongoose, Async

Using pokemon module

  • installing pokemon module by using npm install pokemon
shell
╭─ npm install pokemon

added 3 packages, and audited 5 packages in 5s

2 packages are looking for funding
  run `npm fund` for details
  • index.js file
javascript
  const pokemon = require("pokemon");

  console.log(pokemon.all());
  • Output
shell
    [
    'Bulbasaur',  'Ivysaur',    'Venusaur',   'Charmander', 'Charmeleon',
    'Charizard',  'Squirtle',   'Wartortle',  'Blastoise',  'Caterpie',
    'Metapod',    'Butterfree', 'Weedle',     'Kakuna',     'Beedrill',
    'Pidgey',     'Pidgeotto',  'Pidgeot',    'Rattata',    'Raticate',
    'Spearow',    'Fearow',     'Ekans',      'Arbok',      'Pikachu',
    'Raichu',     'Sandshrew',  'Sandslash',  'Nidoran♀',   'Nidorina',
    ... 865 more items
  ]

  Process finished with exit code 0

Using nodemon module

  • nodemon module is a simple monitor script for use during development of a Node.js app
  • installing nodemon globally, by npm install nodemon -g
shell
    ╭─ npm install nodemon -g

  added 32 packages in 2s

  3 packages are looking for funding
    run `npm fund` for details

Creating a NodeJS server

  • index.js file
javascript
  const http = require("http");
  const PORT = 4000;
  const HOST = "localhost";

  const server = http.createServer((request, response) => {
    response.end("Working...");
  });

  server.listen(PORT, HOST, () => {
    console.log(`Server is working on http://${HOST}:${PORT}`);
  });
  • Terminal
shell
  Server is working on http://localhost:4000
  • Localhost : 4000

Routing using NodeJS Server

  • index.html file
html
  <!DOCTYPE html>
  <html lang="en">
    <head>
      <meta charset="UTF-8" />
      <meta
        name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"
      />
      <meta http-equiv="X-UA-Compatible" content="ie=edge" />
      <title>Document</title>
      <style>
        html {
          background-color: #1e2537;
          color: white;
          height: 100vh;
          font-family: Arial;
        }
      </style>
    </head>
    <body>
      <div className="home">
        <h1>Home Section</h1>
      </div>
    </body>
  </html>
  • route.js file
javascript
  const http = require("http");
  const fs = require("fs");

  const PORT = 4000;
  const HOST = "localhost";

  const home = fs.readFileSync("./index.html", "utf-8");

  const server = http.createServer((request, response) => {
    if (request.url === "/") {
      response.end(home);
    } else if (request.url === "/about") {
      response.end("<h1 style='font-family: Arial'>About Page</h1>");
    } else {
      response.end(
        "<h1 style='font-family: Arial; color: #FC6E68'>404 Page Not Found</h1>"
      );
    }
  });

  server.listen(PORT, HOST, () => {
    console.log(`Server is working on http://${HOST}:${PORT}`);
  });
  • LocalHost: 4000

Deploying the NodeJS server

  • npm start command to work, add "start": node ./server/route.js in "scripts" : {} object in package.json file
json
  {
    "name": "00-basics",
    "version": "1.0.0",
    "description": "learning nodeJS",
    "main": "modules/file-based/index.js",
    "scripts": {
      "start": "node ./server/index.js",
      "test": "echo \"Error: no test specified\" && exit 1"
    },
    "author": "",
    "license": "ISC",
    "devDependencies": {
      "prettier": "2.8.7"
    },
    "dependencies": {
      "pokemon": "^2.3.4"
    }
  }
  • Output
shell
  ╭─ npm start

  > 00-basics@1.0.0 start
  > node ./server/index.js

  Server is working on http://localhost:4000