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More details in the official Node.js docs - [About Node.js](https://nodejs.org/en/about)

**Node.js** is a JavaScript runtime outside the browser, built on Google Chrome's **V8** engine.
It lets you run JavaScript code on the server, not just in the browser.

### Core characteristics

1. **Runtime**
Node.js is not a language or a framework, it is the **environment** in which JS code runs.
2. **The V8 engine**
Node.js is built on the V8 engine, written in C++, which compiles JavaScript into machine code for high execution speed.
3. **Single-threaded with non-blocking I/O**
Node.js runs in a single thread but efficiently handles thousands of requests at once thanks to **asynchrony** and the **event loop**.
4. **Modularity**
It uses the CommonJS module system (`require`, `module.exports`) and ES modules (`import`, `export`).
5. **The npm package manager**
Node.js ships with **npm (Node Package Manager)**, the largest repository of JavaScript libraries.

### Uses of Node.js

- Building **web servers** (for example with Express.js, NestJS, Fastify)
- Building **REST APIs** and **GraphQL APIs**
- Building **real-time** applications (chats, online games, notifications)
- **CLI tools** and automation scripts
- **SSR (Server-Side Rendering)** for React, Next.js and others
- **Microservices** and backend logic

### A simple HTTP server in Node.js

```javascript
const http = require('http');

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

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

### Key advantages

- High performance (V8 + non-blocking I/O)
- Simple to work with JSON and REST
- One language - JavaScript on the client and the server
- A large npm package ecosystem
- Support for microservice and event-driven architectures

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