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## 1. Main role: running JavaScript code

V8 is the **JavaScript engine**, written in C++, created by Google for the Chrome browser.
Node.js embeds it to run JS not in a browser, but on the server.

When you run:

```javascript
node app.js
```

Node.js hands the code of `app.js` to the V8 engine, which **parses, compiles and runs it**.

## 2. Compiling to machine code

- V8 **does not interpret JavaScript line by line**, like older engines did.
- It uses **JIT compilation (Just-In-Time)**: it turns JS into machine code that the CPU runs directly.
- This makes code execution **very fast**, close to native languages like C and C++.

Inside V8:

- **Parser**: analyzes the source code.
- **Ignition**: the bytecode interpreter.
- **TurboFan**: the optimizing compiler (produces machine code and optimizes frequently called functions).

## 3. Memory management and garbage collection

V8 is responsible for:

- allocating memory for objects, arrays, functions and closures;
- automatically freeing memory through the garbage collector (GC);
- optimizing how the heap and the stack are used.

This frees developers from having to manage memory manually, unlike in C++.

## 4. Integration with the Node.js C++ core

Node.js exposes native APIs (for example, `fs`, `net`, `http`) written in C++, and V8 provides the "bridge" between JS and C++:

- When JS code calls, say, `fs.readFile()`, V8:
  1. interprets the JS function call;
  2. passes it to the C++ implementation through **bindings**;
  3. gets the result back and returns it to the JS world.

## 5. The link with the Event Loop

- V8 runs synchronous JS code and the callbacks that come from the **Event Loop** (implemented in libuv).
- In other words, V8 handles **running the code**, while libuv handles **asynchrony and events**.

## 6. V8 as the foundation of every JS object

- All of JS's base objects (Array, Object, Function, Map, and so on) are implemented inside V8.
- So when you create `const arr = []`, V8 creates the corresponding object in its own memory and manages it.

## 7. An example execution flow

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

fs.readFile('data.txt', 'utf-8', (err, data) => {
  console.log(data);
});
```

1. V8 runs the JS code up to the `readFile` call.
2. Node.js (through bindings) hands the `fs.readFile` operation to C++ and libuv.
3. When the operation finishes, libuv passes the callback back to V8.
4. V8 runs the callback (`console.log(data)`).

## Summary

| Role | Description |
|---|---|
| Running code | Interpretation and JIT compilation of JS into machine code |
| Optimization | TurboFan optimizes frequently used functions |
| Garbage collection | Automatically clears unused memory |
| Link to C++ | Provides the interface between JS and Node.js's native modules |
| Runtime environment | Implements base objects, functions, prototypes and the JS standard |

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