Node.js Internals and Architecture

Basic

1.Javascript is single thread.
2.Every Browsers have java script engine.
3.JS work different in both environment Node.js and Browser

What is Node.JS?

Node.js is a runtime environment that allows JavaScript to run outside the browser. It is built on Chrome’s V8 JavaScript engine and uses an event-driven, non-blocking I/O architecture which makes it highly efficient for scalable applications.

'V8' + 'C++' + 'LIBUV' is Node.js

1️⃣ V8 Engine (JavaScript Engine)

The V8 engine executes JavaScript code.

Key Functions

1.Converts JavaScript → Machine Code
2.Executes the code very fast using Just-In-Time (JIT) compilation
3.Handles memory management and garbage collection

2️⃣ Node.js Bindings (C/C++ Layer)

Node.js bindings act as a bridge between JavaScript and C/C++ libraries.

Why they exist

JavaScript alone cannot directly access system-level features like:

1.File system
2.Network
3.OS operations

What bindings do

They connect JavaScript APIs to native C/C++ implementations.

Example:

fs.readFile()

Flow:

JavaScript → Node.js API → C++ Bindings → libuv / OS

3️⃣ Libuv (Core Asynchronous Engine)

libuv is a C library that handles asynchronous operations.

Responsibilities

1.Event Loop
2.Thread Pool
3.File system operations
4.Network I/O
5.DNS operations
6.Child processes

libuv allows Node.js to perform non-blocking I/O operations.

Example:

Reading files
Database calls
API requests

Instead of blocking the thread, these operations run in background threads.

4️⃣ Event Loop

The Event Loop manages asynchronous tasks.

It continuously checks:

• Is there any callback waiting?

• Is any operation completed?

Event Loop Phases

1.Exipred Callback()
2. IO Polling()
3. SetImmediate()
4. Close Callback()

while true{
  1.expriedcallback()->set timeout(()=>{},2)
  2.IO Polling->file reading Operation callback
  3.setimmediate()->only available in node.js
  4.close callbacks()
  5.check if anything pending? 
  No=exit 
  yes=continue
}

5️⃣ Thread Pool

Node.js uses a thread pool (4 threads by default) for operations like:

• File system operations

• DNS lookup

• Compression

• Cryptography

Example:

fs.readFile()
crypto.pbkdf2()

These run in the libuv thread pool instead of blocking the main thread.

6️⃣ Execution Flow in Node.js

Example code:

import fs from 'fs';
import crypto from 'crypto';

const start = Date.now();

process.env.UV_THREADPOOL_SIZE = 4;

setTimeout(() => console.log('Hello from Timer'), 0);
setImmediate(() => console.log('Hello from Immediate'), 0);

fs.readFile('sample.txt', 'utf-8', function (err, data) {
  console.log(`File Reading Complete...`);

  setTimeout(() => console.log('Time 2'), 0);
  setTimeout(() => console.log('Time 3'), 0);
  setImmediate(() => console.log('Immediate 2'), 0);

  crypto.pbkdf2('password', 'salt', 300000, 1024, 'sha256', () => {
    console.log('Password 1 has been hashed', Date.now() - start);
  });

  crypto.pbkdf2('password', 'salt', 300000, 1024, 'sha256', () => {
    console.log('Password 2 has been hashed', Date.now() - start);
  });

  crypto.pbkdf2('password', 'salt', 300000, 1024, 'sha256', () => {
    console.log('Password 3 has been hashed', Date.now() - start);
  });

  crypto.pbkdf2('password', 'salt', 300000, 1024, 'sha256', () => {
    console.log('Password 4 has been hashed', Date.now() - start);
  });

  crypto.pbkdf2('password', 'salt', 300000, 1024, 'sha256', () => {
    console.log('Password 5 has been hashed', Date.now() - start);
  });
});

console.log('Hello from Top Level Code');

Execution order

Hello from Top Level Code
Hello from Timer
File Reading Complete...
Hello from Immediate
Immediate 2
Time 2
Time 3
Password 2 has been hashed 8047
Password 3 has been hashed 8047
Password 1 has been hashed 8156
Password 4 has been hashed 8436
Password 5 has been hashed 9959