Event-driven programming kya hoti hai Node.js me?

Node.js me event-driven programming ek aisa programming style hai jisme code ka execution events ke respond karne par hota hai, instead of sequentially line-by-line. Matlab, kuch action hone par (jaise request aana, file read hona, ya button click) event trigger hota hai aur uske corresponding function (callback) execute hota hai.

🔹 Key Points:

1. Events ka concept
   • Node.js me events hoti hain jaise data received, connection established, error occurred.
   • Har event ke liye aap listener define kar sakte ho.
2. Event Emitter
   • Node.js me EventEmitter class hai jo events create aur handle karne me help karta hai.
   • Aap events ko emit karte ho aur usko listener se handle karte ho.

🔹 Example:

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

// Event listener
myEmitter.on('greet', (name) => {
    console.log(`Hello, ${name}!`);
});

// Event trigger (emit)
myEmitter.emit('greet', 'Tirithraj');

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

// Event listener
myEmitter.on('greet', (name) => {
    console.log(`Hello, ${name}!`);
});

// Event trigger (emit)
myEmitter.emit('greet', 'Tirithraj');

Output:

Hello, Tirithraj!

Hello, Tirithraj!

• greet event ko trigger karte hi uska listener run hua.

🔹 Node.js me Event-driven programming ka use

• Server Requests: Jab HTTP request aati hai, server event trigger karta hai aur response send karta hai.
• Streams: Data chunks aane par event trigger hota hai.
• Asynchronous Operations: File read, DB query, network request me callback ke through event-driven execution hota hai.