Node js

How to run node js program

Install node js application

open command prompt

then enter this commands

node --version

mkdir testApp

cd testApp

npm init -y

save this code in C:\Users\CDU\testApp

//app.js

const http = require('http')

const port = 8080

// Create a server object:

const server = http.createServer(function (req, res) {

    // Write a response to the client

    res.write('Hello World')

    // End the response 

    res.end()

})

// Set up our server so it will listen on the port

server.listen(port, function (error) {

    // Checking any error occur while listening on port

    if (error) {

        console.log('Something went wrong', error);

    }

    // Else sent message of listening

    else {

        console.log('Server is listening on port' + port);

    }

})

save this file as app.js

run this command in command prompt

node app.js

Output: Now open your browser and go to http://localhost:8080/, you will see the following output.

How to create a chat app using nodejs

Open command prompt enter these commands

mkdir socket-chat-app
cd socket-chat-app

npm init -y

npm install express socket.io

touch index.html index.js

Save this program as index.html in C:\Users\CDU\socket-chat-app

<!DOCTYPE html> 

<html> 

<head> 

<title>Chat app using Socket IO and Node JS</title> 

<script src="https://cdn.tailwindcss.com"></script> 

</head> 

<body> 

<h1 class="font-bold text-green-500 

text-3xl text-center mt-5"> 

GeeksforGeeks 

</h1> 

<div> 

<h2 class="font-semibold text-xl 

text-center mt-5" 

id="logo"> 

Chat App using Socket io 

</h2> 

</div> 

<form class="flex flex-col justify-center 

items-center mt-5" 

id="form"> 

<input class="border border-gray-400 

rounded-md mt-5 p-1" 

type="text"

placeholder="Name"

id="myname"> 

<input class="border border-gray-400 

rounded-md mt-5 p-1" 

type="text"

placeholder="Message"

id="message"> 

<button class="bg-blue-500 rounded-md p-2 

text-white mt-5"> 

Send 

</button> 

</form> 

<div class="flex flex-col justify-center 

items-center mt-5" 

id="messageArea"> 

</div> 

</body> 

<script src="/socket.io/socket.io.js"></script> 

<script> 

let socket = io(); 

let form = document.getElementById('form'); 

let myname = document.getElementById('myname'); 

let message = document.getElementById('message'); 

let messageArea = document.getElementById("messageArea"); 

form.addEventListener("submit", (e) => { 

e.preventDefault(); 

if (message.value) { 

socket.emit('send name', myname.value); 

socket.emit('send message', message.value); 

message.value = ""; 

} 

}); 

socket.on("send name", (username) => { 

let name = document.createElement("p"); 

name.style.backgroundColor = "grey"; 

name.style.width = "100%"; 

name.style.textAlign = "center"; 

name.style.color = "white"; 

name.textContent = username + ":"; 

messageArea.appendChild(name); 

}); 

socket.on("send message", (chat) => { 

let chatContent = document.createElement("p"); 

chatContent.textContent = chat; 

messageArea.appendChild(chatContent); 

}); 

</script> 

</html>

Save this file as index.js

const express = require('express'); 

const app = express(); 

const { Server } = require('socket.io'); 

const http = require('http'); 

const server = http.createServer(app); 

const io = new Server(server); 

const port = 5000; 

app.get('/', (req, res) => { 

res.sendFile(__dirname + '/index.html'); 

}); 

io.on('connection', (socket) => { 

socket.on('send name', (username) => { 

io.emit('send name', (username)); 

}); 

socket.on('send message', (chat) => { 

io.emit('send message', (chat)); 

}); 

}); 

server.listen(port, () => { 

console.log(`Server is listening at the port: ${port}`); 

});

node index.js

Output: Open your browser and open two tabs with the URL: http://localhost:5000 so that we have two clients that can chat with each other.

QR Code Generator code

https://www.geeksforgeeks.org/qr-code-generator-service-with-node-js-and-express-js/

Prerequisites

• Node.js and npm (or yarn) installed
• Basic understanding of Node JS, Express JS, and JavaScript

Now open command prompt and these commands

mkdir qr-code-generator
cd qr-code-generator

mkdir server
cd server   
npm init -y

npm install express qrcode body-parser cors

These 4 programs for server side

Now create a folder in c: users/cdu/server and save these code as app.js

//app.js

const express = require('express');

const bodyParser = require('body-parser');

const cors = require('cors');

const router = require('./routes');

const app = express();

const port = process.env.PORT || 3000;

app.use(bodyParser.json());

app.use(cors());

app.use(router);

app.listen(port, () => {

console.log(`Server listening on port ${port}`);

});

Save this code as controller.js

//controller.js

const service = require('./service');

exports.generateQR = async (req, res) => {

try {

const { data } = req.body;

const qrCodeText = service.formatData(data);

const qrCodeBuffer = await service.generateQRCode(qrCodeText);

res.setHeader('Content-Disposition', 'attachment; filename=qrcode.png');

res.type('image/png').send(qrCodeBuffer);

} catch (err) {

console.error('Error generating QR code:', err);

res.status(500).send({ error: 'Internal Server Error' });

}

};

Save this code as routes.js

//routes.js

const express = require('express');

const controller = require('./controller');

const router = express.Router();

router.post('/generate-qr', controller.generateQR);

module.exports = router;

Save this code as service.js

//service.js

const QRCode = require('qrcode');

exports.formatData = (data) => {

const qrCodeText = `Product ID: ${data.id}, Price: $${data.price}`;

return qrCodeText;

};

exports.generateQRCode = async (qrCodeText) => {

const options = {

errorCorrectionLevel: 'M',

type: 'image/png',

margin: 1

};

const qrCodeBuffer = await QRCode.toBuffer(qrCodeText, options);

return qrCodeBuffer;

};

Now These 3 programs for client side

Create a new folder in c: users/cdu/clients

Save this file as index.html 

<!-- index.html -->

<!DOCTYPE html>

<html lang="en">

<head>

<meta charset="UTF-8">

<meta name="viewport" content="width=device-width, initial-scale=1.0">

<title>QR Code Generator</title>

<link rel="stylesheet" href="style.css">

</head>

<body>

<h1>QR Code Generator</h1>

<form id="qr-form">

<div class="content">

<label for="qr-id" class="margin">ID:</label>

<input type="text" id="qr-id" class="qr-input" placeholder="Enter ID">

</div>

<div class="content">

<label for="qr-price">Price:</label>

<input type="text" id="qr-price" class="qr-input" placeholder="Enter Price">

</div>

<button type="submit" class="content">Generate QR Code</button>

</form>

<div id="qr-result">

</div>

<script src="script.js"></script>

</body>

</html>

Save this file as style.css 

/* style.css */

body {

font-family: Arial, sans-serif;

text-align: center;

margin-top: 50px;

}

.content {

margin-bottom: 15px;

}

.margin {

margin-right: 18px;

}

.qr-input {

padding: 10px;

width: 200px;

}

#qr-result img {

margin-top: 20px;

border: 1px solid #000;

}

button {

padding: 10px 12px;

text-transform: uppercase;

border-radius: 5px;

background-color: bisque;

}

Save this file as script.js

// script.js

document.getElementById('qr-form').addEventListener('submit', function (e) {

e.preventDefault();

const id = document.getElementById('qr-id').value;

const price = document.getElementById('qr-price').value;

const data = { id, price }

fetch('http://localhost:3000/generate-qr', {

method: 'POST',

headers: {

'Content-Type': 'application/json',

},

body: JSON.stringify({ data })

})

.then(response => response.blob())

.then(blob => {

const qrImage = document.createElement('img');

const qrImageUrl = URL.createObjectURL(blob);

qrImage.src = qrImageUrl;

const qrResultDiv = document.getElementById('qr-result');

qrResultDiv.innerHTML = '';

qrResultDiv.appendChild(qrImage);

})

.catch(error => console.error('Error generating QR code:', error));

});

To get output enter this command in command prompt

node app.js

http://localhost:3000/