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1.2.1 • Public • Published


NPM version NPM downloads jsDelivr (npm)

Ultra-flexible & dead simple event emitter supporting RegExp-based event subscription and global listeners.


$ npm install --save @qoopido/emitter # npm
$ yarn add @qoopido/emitter           # yarn


The only thing left to do after installation via NPM or yarn is to require the module:

$ import Emitter from '@qoopido/emitter';      // esm
$ const Emitter = require('@qoopido/emitter'); // cjs

Afterwards you can either create an instance or extend Emitter with your own class and use its methods as described below.


Listeners (also referred to as callbacks) must be of type Function which will always receive an instance of type Event as their first parameter. If the event was emitted with further parameters these will be passed to the listener as separate arguments.

The passed Event instance offers access to the event name as well as its context and, in addition, offers a cancel method to stop further processing of an event.

Subscribing to events

The emitter offers a total of three methods to subscribe to events: on, once and limit.

// register an event listener
emitter.on({String|RegExp|(String|RegExp)[]} identifier, {Function} callback, {Boolean=} prepend, {Number=} limit);

// register a once only event listener
emitter.once({String|RegExp|(String|RegExp)[]} identifier, {Function} callback, {Boolean=} prepend);

// register an event listener that gets called a limited number of times
emitter.limit({String|RegExp|(String|RegExp)[]} identifier, {Number} limit, {Function} callback);

identifier can either be a specific event name as String, a pattern of event names as RegExp or an array of both which gives you almost endless flexibitlity.

Unsubscribing from events

The only method to know is the off method:

emitter.off({String|RegExp|(String|RegExp)[]} identifier, {Function=} callback);

identifier can, again, either be a specific event name as String, a pattern of event names as RegExp or an array of both. Just keep in mind that unsubscribing from a specific event name will never unsubscribe a RegExp-listener and vice versa.

Emitting events

Any instance of Emitter has its own emit method:

emitter.emit({String} name, ...details);

Retrieving listeners

If you need to retrieve any existing listener for a specific event simply use

emitter.listener({String} name);

Calling listener will always return an array which may be empty.


Any method beside listener returns the current instance to offer a chainable interface.

Broadcast listeners

It is possible to not only subscribe to events emitted by a known instance of Emitter but also to subscribe to events emitted by any existing and/or future instance. This behaviour allows, e.g., to subscribe to events globally for logging purposes and the likes.

var Emitter = require('@qoopido/emitter');

// register a broadcast listener
Emitter.on({String|RegExp|(String|RegExp)[]} identifier, {Function} callback, {Boolean=} prepend, {Number=} limit);

// register a once only broadcast listener
Emitter.once({String|RegExp|(String|RegExp)[]} identifier, {Function} callback, {Boolean=} prepend);

// register a broadcast listener that gets called a limited number of times
Emitter.limit({String|RegExp|(String|RegExp)[]} identifier, {Number} limit, {Function} callback);

// unregsiter a broadcast listener
Emitter.off({String|RegExp|(String|RegExp)[]} identifier, {Function=} callback);

// retrieve boradcast listeners for a specific event
Emitter.listener({String} name);


npm i @qoopido/emitter

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