Evemit

Minimal and fast JavaScript / TypeScript event emitter for Node.js, Bun.js, Deno and front-end.
Only 1kb minified (577 bytes gzipped).

Used in prod on several projects (front-end and back-end) for over 10 years, very stable. API does not change, no breaking changes. 🚀

Getting started

Install

Via NPM

npm install evemit --save

Or download the evemit.min.js file.

If Evemit is used in ESM or CommonJS environment (Node.js, Vite.js, Webpack, ...), it is exposed as module with module.exports.

So in CommonJS and ES Modules, evemit is not exposed in the global scope (even on client side) :)

import ev from 'evemit';
// or const ev = require('evemit');

// true (it's the constructor)
console.log(typeof ev === 'function');

// undefined, even on front-end with Browserify, Webpack, ...
console.log(typeof Evemit);

Basic usage (without builder)

// true
console.log(typeof Evemit === 'function');

// true
console.log(typeof window.Evemit === 'function');

Usage

import Evemit from 'evemit';

// Or if you are not in an environment CommonJS (Node.js, Browserify, Webpack, ...)
// uses directly `Evemit`, without `var Evemit = require('evemit')`

const obj = new Evemit();

obj.on('say-hello', function(hello) {
  console.log(hello); // Hello World!
});

obj.emit('say-hello', 'Hello World!');

API

See the complete API doc.

Evemit.on({string} event, {function} listener, {mixed} [context])

Add a listener.

obj.on('say-hello', function(hello) {
  console.log(hello); // Hello World!
});

obj.emit('say-hello', 'Hello World!');

Evemit.once({string} event, {function} listener, {mixed} [context])

Listen once

function myCallback(data) {
  console.log(data.hello); // Hello 1
}

// Add listener, defined to be triggered "once"
obj.once('say-hello', myCallback);

// myCallback() is invoked and the listener is removed
obj.emit('say-hello', {
  hello: 'Hello 1'
});

// myCallback() is not called because it is no longer listening on this event
obj.emit('say-hello', {
  hello: 'Hello 2'
});

Evemit.emit({string} event, {mixed} [...arg])

Emit an event

obj.emit('ping');

With arguments passed to the listeners

obj.emit('ping', 'arg1', 'arg2', {an: 'object'});

Evemit.off({string} event, {function} listener)

Remove a listener

function myCallback(data) {
  // some code ...
}

// add
a.on('say-hello', myCallback);

// remove
a.off('say-hello', myCallback);

Evemit.listeners({string} [event])

Get all listeners

// Returns an array containing all listeners
obj.listeners();

Count all listeners

// Returns a number.
obj.listeners().length;

Get all listeners of a given event

// Returns an array of listeners
obj.listeners('say-hello');

Count all listeners of a given event

obj.listeners('say-hello').length;

The methods of the Array object can be used to manage the listeners.

Example

// reverse the order of the listeners execution
obj.listeners('my-event').reverse();

// slices
obj.listeners('my-event').slice(1, 3);

// Removes the first listener of the stack, and returns that listener
const firstListener = obj.listeners('my-event').shift();

// Removes the last listener of the stack, and returns that listener
const lastListener = obj.listeners('my-event').pop();

// ...

Use the property obj.events if you want to get an object like

{event1: [array of listeners], event2: [array of listeners], ...}

Unit tests

evemit is unit tested with Unit.js.

Run the tests

cd node_modules/evemit

npm test

To execute the tests on client side, download the test directory and go on test/index.html file with your browser.

LICENSE

MIT (c) 2014, Nicolas Tallefourtane.

Author

Nicolas Talle