1. What is Node.js?

Node.js is a JavaScript runtime built on Chrome's V8 engine, enabling server-side scripting with JavaScript. It is designed for building scalable network applications and is especially useful for I/O-heavy applications like web servers.

2. Setting Up Node.js

To get started with Node.js, download and install it from the official website: Node.js.

Verify the installation by running:

node -v

3. Your First Node.js Application

Create a simple Node.js application that listens to requests on a specified port:

const http = require('http');

const server = http.createServer((req, res) => {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello, Node.js!');
});

server.listen(3000, '127.0.0.1', () => {
    console.log('Server running at http://127.0.0.1:3000/');
});

Run this file with:

node app.js

4. Working with Modules

Node.js has a rich set of built-in modules that can be used for various tasks. For example, you can use the fs module to interact with the file system:

const fs = require('fs');

fs.readFile('example.txt', 'utf8', (err, data) => {
    if (err) throw err;
    console.log(data);
});

5. File System Operations

Node.js provides asynchronous and synchronous methods for file operations. Here’s how to read a file asynchronously:

fs.readFile('example.txt', 'utf8', (err, data) => {
    if (err) throw err;
    console.log(data);
});

For synchronous operations:

const data = fs.readFileSync('example.txt', 'utf8');
console.log(data);

6. HTTP Server

Node.js is commonly used to create HTTP servers. Here's a basic HTTP server example:

const http = require('http');

const server = http.createServer((req, res) => {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/html');
    res.end('
Hello from Node.js Server!
');
});

server.listen(3000, '127.0.0.1', () => {
    console.log('Server running at http://127.0.0.1:3000/');
});

7. Express.js Framework

Express.js is a minimalist web framework for Node.js, often used to handle routing and HTTP methods. To get started with Express:

npm install express

Example of a simple Express server:

const express = require('express');
const app = express();

app.get('/', (req, res) => {
    res.send('Hello, Express!');
});

app.listen(3000, () => {
    console.log('Server running at http://127.0.0.1:3000/');
});

8. Handling POST Requests

Use Express to handle POST requests by adding the body-parser middleware to parse the request body:

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

app.use(bodyParser.json());

app.post('/submit', (req, res) => {
    const { name, age } = req.body;
    res.send(`Received: ${name}, ${age}`);
});

app.listen(3000, () => {
    console.log('Server running at http://127.0.0.1:3000/');
});

9. Middleware

Middleware functions in Express are used to process requests before they reach the route handlers. Here's an example of custom middleware:

app.use((req, res, next) => {
    console.log(`Request received at ${req.url}`);
    next();
});

10. Running Node.js in Production

To run Node.js applications in production, it's important to use a process manager like PM2:

npm install pm2 -g
pm2 start app.js --name "my-app"
pm2 save

PM2 will keep your application running even after a server restart and allows easy monitoring and management of your app.