Core Node.js Fundamentals

5.1 The Event Loop: How Node.js Works

Node.js is single-threaded, but it can handle thousands of tasks at the same time thanks to its event loop.

Why Is This Special?

Node.js doesn’t block other tasks while waiting for things like file reads, database queries, or API calls to finish.

Instead, it uses a non-blocking approach with the event loop, allowing it to be highly scalable and efficient.

Real-World Analogy

Imagine you are a chef in a one-man kitchen. When customers place orders:

  • You hand tasks to your assistants (like boiling water or chopping veggies).
  • You don’t wait, you move on to the next order.
  • When an assistant finishes, they notify you (callback), and you serve the food.

That’s how Node.js handles I/O tasks, by delegating and moving on to other tasks.

How Node.js Event Loop Works

  1. Receives a Task
    For example: reading a file, making an HTTP request.

  2. Delegates the Task
    Node sends it to the Operating System or libuv thread pool to handle it.

  3. Registers a Callback
    This is a function to be run when the task is done.

  4. Continues Executing
    The main thread does not wait, it continues with the next task.

  5. Handles Completion
    When the task completes, its callback is added to a callback queue.

  6. Event Loop Picks It Up
    If the call stack is clear, the event loop executes the callback.

This entire mechanism is what makes Node.js non-blocking.

5.2 Node.js Architecture Explained

Node.js is built on top of several key layers:

1. V8 Engine

V8 engine is developed by Google and its used in Google Chrome. It converts JavaScript into fast machine code

2. Libuv

Libuv is a C library that provides:

  • Event loop:
  • Thread pool
  • Async I/O

3. Event Loop

Event Loop manages the execution of callbacks. It is the core of Node.js's non-blocking model.

4. C++ Bindings

C++ Bindings connects Node.js code to system-level operations (files, network, etc.)

5. Node.js APIs

Node.js APIs are built-in modules like:

  • fs (File System)
  • http (Server)
  • path (Utilities)

These APIs allow JavaScript to do things it can’t do in the browser, like read/write files or listen on a server port.

PS: I will make a video on this topic in the future because text can't do justice to its explanation

5.3 Modules in Node.js

Modules are building blocks in Node.js. Instead of writing one long file, you break your code into smaller, reusable files.

Types of Modules

  • Core Modules – Built into Node.js (e.g., fs, http, path)
  • Local Modules – Files you create yourself
  • Third-party Modules – Installed via npm (e.g., express, lodash)

Using a Module

// math.js
function add(a, b) {
  return a + b;
}
module.exports = add;

// app.js
const add = require("./math");
console.log(add(2, 3)); // 5

Modules help organize and scale your application more effectively.