emitter-component

What is emitter-component?

The emitter-component npm package is a simple event emitter implementation. It allows you to create objects that can emit events and have listeners that respond to those events. This is useful for decoupling different parts of an application and enabling communication between them.

What are emitter-component's main functionalities?

Event Emission

This feature allows you to emit events and have listeners respond to those events. In the code sample, an event listener is defined for the 'event' event, and then the event is emitted with a message.

const Emitter = require('emitter-component');
const emitter = new Emitter();

// Define an event listener
emitter.on('event', function(message) {
  console.log('Event received:', message);
});

// Emit an event
emitter.emit('event', 'Hello, World!');

Removing Event Listeners

This feature allows you to remove event listeners. In the code sample, an event listener is defined and then removed before the event is emitted, so no listeners respond to the event.

const Emitter = require('emitter-component');
const emitter = new Emitter();

function onEvent(message) {
  console.log('Event received:', message);
}

// Define an event listener
emitter.on('event', onEvent);

// Remove the event listener
emitter.off('event', onEvent);

// Emit an event (no listeners should respond)
emitter.emit('event', 'Hello, World!');

Once Event Listeners

This feature allows you to define event listeners that will be called only once. In the code sample, the event listener is defined with the 'once' method and is called only the first time the event is emitted.

const Emitter = require('emitter-component');
const emitter = new Emitter();

// Define an event listener that will be called only once
emitter.once('event', function(message) {
  console.log('Event received:', message);
});

// Emit the event twice
emitter.emit('event', 'Hello, World!');
emitter.emit('event', 'Hello again!');

Other packages similar to emitter-component

events

The 'events' package is the built-in Node.js event emitter module. It provides a similar API to emitter-component but is more feature-rich and is maintained as part of the Node.js core. It is widely used and well-documented.

eventemitter3

The 'eventemitter3' package is a high-performance event emitter for Node.js and the browser. It is similar to emitter-component but offers better performance and additional features like wildcard event listeners.

mitt

The 'mitt' package is a tiny (~200 bytes) functional event emitter. It is similar to emitter-component but is designed to be extremely lightweight and simple, making it suitable for use in performance-critical applications.

README

Emitter

Event emitter component.

Installation

$ component install component/emitter

API

Emitter(obj)

The Emitter may also be used as a mixin. For example a "plain" object may become an emitter, or you may extend an existing prototype.

As an Emitter instance:

var Emitter = require('emitter');
var emitter = new Emitter;
emitter.emit('something');

As a mixin:

var Emitter = require('emitter');
var user = { name: 'tobi' };
Emitter(user);

user.emit('im a user');

As a prototype mixin:

var Emitter = require('emitter');
Emitter(User.prototype);

Emitter#on(event, fn)

Register an event handler fn.

Emitter#once(event, fn)

Register a single-shot event handler fn, removed immediately after it is invoked the first time.

Emitter#off(event, fn)

Remove event handler fn, or pass only the event name to remove all handlers for event.

Emitter#emit(event, ...)

Emit an event with variable option args.

Emitter#listeners(event)

Return an array of callbacks, or an empty array.

Emitter#hasListeners(event)

Check if this emitter has event handlers.