Understanding Event Emitters in Node.js: How and When to Use Them

What Are Event Emitters in Node.js?

Event Emitters in Node.js are a core part of its asynchronous, event-driven architecture. They allow communication between different parts of an application by emitting named events and responding to them with registered callback functions.

How Do Event Emitters Work?

• Node.js provides the events module with the EventEmitter class.
• Objects derived from EventEmitter can register event listeners and emit events asynchronously.
• Listener functions execute each time the event is emitted.

Example: Basic Usage

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

// Registering an event listener
emitter.on('greet', (name) => {
    console.log(`Hello, ${name}!`);
});

// Emitting the event
emitter.emit('greet', 'Alice'); // Output: Hello, Alice!

Common Use Case: Custom Logging System

Suppose you need a custom logging solution across different components:

• Create a logger that emits events when something should be logged.
• Attach listeners to process or store those log events.

Example

const EventEmitter = require('events');
class Logger extends EventEmitter {
    log(message) {
        this.emit('log', message);
    }
}

const logger = new Logger();

// Listen for log events
logger.on('log', (msg) => {
    console.log(`Log: ${msg}`);
});

logger.log('Server started'); // Output: Log: Server started

---

Summary:

• Use Event Emitters for loosely coupled communication between different parts of a Node.js application.
• Ideal for custom events, streaming APIs, or building modular systems.

You can extend or reuse EventEmitter to create powerful, modular Node.js applications.