Node.js Events & Event Loop | asadmukhtar.info

Node.js Events & Event Loop | asadmukhtar.info

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Node.js Events & Event Loop

🔹 Node.js Events

Node.js has a built-in events module that allows us to work with event-driven programming. Events in Node.js are similar to browser events but are used in a server-side environment.

The EventEmitter class is used to create and handle custom events.
We can emit (trigger) and listen for events.

Example: Using Events in Node.js

const EventEmitter = require('events');
const event = new EventEmitter();

// Creating an event listener
event.on('greet', () => {
    console.log('Hello! Welcome to Node.js Events.');
});

// Emitting (triggering) the event
event.emit('greet');

Node.js Event Loop

The Event Loop is the heart of Node.js. It allows Node.js to handle asynchronous operations without blocking the main thread.

📌 How It Works:

Call Stack: Executes synchronous code first.
Event Queue: Stores asynchronous callbacks (like setTimeout, I/O operations).
Microtask Queue: Handles Promises and process.nextTick().
Event Loop: Continuously checks if the call stack is empty and processes the next task.

Example: Understanding the Event Loop

console.log("Start");

setTimeout(() => {
    console.log("Inside setTimeout");
}, 0);

Promise.resolve().then(() => console.log("Inside Promise"));

console.log("End");

Expected Output:

Start
End
Inside Promise
Inside setTimeout

Why?

Synchronous code runs first (Start and End).
Promises (Microtask Queue) execute before setTimeout (Task Queue).

🔹 Summary

Concept	Description
Events	Node.js uses `EventEmitter` to create and handle events.
Event Loop	Manages asynchronous tasks using a non-blocking I/O model.
Call Stack	Executes synchronous code first.
Event Queue	Handles asynchronous callbacks (like `setTimeout`).
Microtask Queue	Processes Promises and `process.nextTick()` faster than the event queue.