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05_node.js

🌐 Create a Server & Read/Write File in Node.js

यह example दिखाता है कि कैसे Node.js में एक HTTP server बनाया जाए और fs module का इस्तेमाल करके file read/write किया जाए।

Example Code

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

// Create HTTP Server
const server = http.createServer((req, res) => {
    if (req.url === '/write') {
        // Write to file
        fs.writeFile('example.txt', 'Hello from Node.js!', (err) => {
            if (err) {
                res.writeHead(500, { 'Content-Type': 'text/plain' });
                return res.end('❌ Error writing file.');
            }
            res.writeHead(200, { 'Content-Type': 'text/plain' });
            res.end('✅ File written successfully.');
        });

    } else if (req.url === '/read') {
        // Read file
        fs.readFile('example.txt', 'utf8', (err, data) => {
            if (err) {
                res.writeHead(500, { 'Content-Type': 'text/plain' });
                return res.end('❌ Error reading file.');
            }
            res.writeHead(200, { 'Content-Type': 'text/plain' });
            res.end(`📄 File Content: ${data}`);
        });

    } else {
        // Default Route
        res.writeHead(200, { 'Content-Type': 'text/plain' });
        res.end('Welcome! Use /write to create a file and /read to read it.');
    }
});

// Start Server
const PORT = 3000;
server.listen(PORT, () => {
    console.log(`🚀 Server running at http://localhost:${PORT}`);
});

"Node.js HTTP Server with Multiple Pages, Common Header, and CSS Support"

📂 Project Structure


project-folder/
│
├── server.js
└── pages/
    ├── header.html
    ├── footer.html
    ├── index.html
    ├── about.html
    ├── contact.html
    └── style.css

Code

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

const PORT = 3000;

http.createServer((req, res) => {
    let filePath = '';
    let contentType = 'text/html';

    // Common header and footer
    const headerHTML = fs.readFileSync(path.join(__dirname, 'pages', 'header.html'), 'utf-8');
    const footerHTML = fs.readFileSync(path.join(__dirname, 'pages', 'footer.html'), 'utf-8');

    // Routing
    if (req.url === '/' || req.url === '/index') {
        filePath = path.join(__dirname, 'pages', 'index.html');
    } 
    else if (req.url === '/about') {
        filePath = path.join(__dirname, 'pages', 'about.html');
    } 
    else if (req.url === '/contact') {
        filePath = path.join(__dirname, 'pages', 'contact.html');
    }
    else if (req.url === '/style.css') {
        filePath = path.join(__dirname, 'pages', 'style.css');
        contentType = 'text/css';
    }
    else {
        res.writeHead(404, { 'Content-Type': 'text/plain' });
        res.end('404 Page Not Found');
        return;
    }

    // Read and send the file
    fs.readFile(filePath, 'utf-8', (err, data) => {
        if (err) {
            res.writeHead(500, { 'Content-Type': 'text/plain' });
            res.end('Internal Server Error');
        } else {
            res.writeHead(200, { 'Content-Type': contentType });

            if (contentType === 'text/html') {
                res.write(headerHTML + data + footerHTML);
            } else {
                res.write(data);
            }
            res.end();
        }
    });

}).listen(PORT, () => {
    console.log(`Server running at http://localhost:${PORT}`);
});

Header File

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>My Website</title>
    <link rel="stylesheet" href="/style.css">
</head>
<body>
    <header>
        <h1>My Node.js Website</h1>
        <nav>
            <a href="/">Home</a> |
            <a href="/about">About</a> |
            <a href="/contact">Contact</a>
        </nav>
    </header>
    <hr>

Footer File

  <hr>
    <footer>
        <p>&copy; 2025 My Website. All Rights Reserved.</p>
    </footer>
</body>
</html>

index File

<main>
    <h2>Welcome to the Home Page</h2>
    <p>This is the homepage of our simple Node.js website.</p>
</main>

about File

<main>
    <h2>About Us</h2>
    <p>We are learning Node.js server-side rendering with static files.</p>
</main>

contact file

<main>
    <h2>Contact Us</h2>
    <p>Email: example@example.com</p>
</main>

css file

body {
    font-family: Arial, sans-serif;
    margin: 20px;
    background: #f2f2f2;
}
header, footer {
    background: #333;
    color: white;
    padding: 10px;
}
header a {
    color: yellow;
    text-decoration: none;
    margin: 0 5px;
}
header a:hover {
    text-decoration: underline;
}
main {
    padding: 10px;
    background: white;
    border-radius: 5px;
}

Run Project

through node

node server.js

Run with Nodemon

Install nodemon globally (only first time):
    npm install -g nodemon
Start the server with nodemon:
    nodemon server.js

📂 File System Related Error Codes

Error Code Meaning When It Happens
ENOENT No such file or directory Jab file/directory exist nahi karti.
EACCES Permission denied Jab file/directory par access permission nahi hota.
EEXIST File already exists Jab file/directory create karte time wo already exist kare.
ENOTDIR Not a directory Jab path directory hona chahiye par file nikle.
EISDIR Is a directory Jab path file hona chahiye par directory ho.
EMFILE Too many open files Jab ek time par system me zyada files open ho jati hain.
EBADF Bad file descriptor Jab galat file descriptor ka use hota hai.

🌐 Network Related Error Codes

Error Code Meaning When It Happens
EADDRINUSE Address already in use Jab server ka port already kisi aur process dwara use ho.
ECONNREFUSED Connection refused Jab server request accept nahi karta.
ECONNRESET Connection reset by peer Jab connection abruptly close ho jata hai (server ya client).
ETIMEDOUT Connection timed out Jab network request ka response time se nahi milta.
EHOSTUNREACH Host unreachable Jab destination host network me available nahi hai.
ENETUNREACH Network unreachable Jab destination network tak pahunch nahi ho rahi.

⚙️ Process & System Related Error Codes

Error Code Meaning When It Happens
ENOMEM Not enough memory Jab system memory khatam ho jaye.
EFAULT Bad address Jab invalid memory address access hota hai.
ESRCH No such process Jab diye gaye PID ka process exist nahi karta.
EPIPE Broken pipe Jab stream close hone ke baad usme likhne ki koshish ho.
EINVAL Invalid argument Jab kisi function ko galat argument diya jata hai.
EPERM Operation not permitted Jab operation ke liye permission nahi hai.

🛠 How to Handle Specific Errors in Node.js

Node.js में errors को handle करने के लिए आपको try...catch blocks (async/await के साथ) या callback में error parameter check करना होता है।

Example: Handling File System Errors

const fs = require('fs');

try {
    fs.readFileSync('data.txt', 'utf8');
    console.log('File read successfully');
} catch (err) {
    if (err.code === 'ENOENT') {
        console.error('❌ File not found. Please check the file path.');
    } else if (err.code === 'EACCES') {
        console.error('❌ Permission denied. Please check file permissions.');
    } else {
        console.error('⚠️ An unexpected error occurred:', err);
    }
}

Example: Handling Network Errors

const http = require('http');

const req = http.get('http://localhost:5000', (res) => {
    console.log(`✅ Status Code: ${res.statusCode}`);
});

req.on('error', (err) => {
    if (err.code === 'ECONNREFUSED') {
        console.error('❌ Connection refused. Is the server running?');
    } else if (err.code === 'ETIMEDOUT') {
        console.error('❌ Request timed out.');
    } else {
        console.error('⚠️ Network error:', err);
    }
});

Example: Handling Process & System Errors

try {
    process.kill(99999); // Invalid PID
} catch (err) {
    if (err.code === 'ESRCH') {
        console.error('❌ Process not found.');
    } else if (err.code === 'EPERM') {
        console.error('❌ Permission denied to kill the process.');
    } else {
        console.error('⚠️ System error:', err);
    }
}

About

This repository contains a collection of practice projects, examples, and exercises focused on Express.js, a minimal and flexible Node.js web application framework. Ideal for developers looking to build RESTful APIs and backend services.

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