Mitty

Simple event emitter for javascript. Enables objects to publish and subscribe to custom events. Works client and server side. Weighs less than 1KB.

Demo and documentation can be found here

With mitty every extended object can publish and listen to custom events. Objects can be both publishers and subscribers simultaneously. Mitty provides a simple api for one object to listen to it's own events or subscribe to some other object events.

Supports all browsers that are ES5-compliant (IE8 and below are not supported).

Examples and api

on and trigger

Subscribe object to events with on(), publish events with trigger().

// start with simple object
var musician = {name: 'George'};

// use "mitty" function to augment object with event api
mitty(musician);

// subscribe to play event
musician.on('play', function(message) {
    console.log(this.name + ' is currently playing. ' + message);
});

// trigger / publish "play" event with custom message as data
// outputs 'George is currently playing. With style!'
musician.trigger('play', 'With style!');

off

Remove events with off()

// Remove subscription
musician.off('play');

// Trigger does nothing since we removed  subscription
musician.trigger('play', 'With style again!');

listenTo and stopListening

Use listenTo() when you want to subscribe to some other object events. Invoke stopListening() when you want to remove those subscriptions.

var instrument = mitty({type: 'Guitar'});

instrument.listenTo(musician, 'play', function() {
    console.log(musician.name + ' is playing ' + this.type + ' with grace!');
});

// Outputs 'George is playing Guitar with grace!'
musician.trigger('play');

// Remove subscription
instrument.stopListening(musician);

// Will not output
musician.trigger('play');

once and listenToOnce

Use once() and listenToOnce() when for executing one time event listeners.

var musician = mitty({name: 'George', playedTimes: 0});

musician.once('play', function() {
    musician.playedTimes += 1;
});

musician.trigger('play').trigger('play').trigger('play');

console.log(musician.playedTimes) // outputs 1

var musician = mitty({name: 'George'});
var instrument = mitty({type: 'Guitar', playedTimes: 0});

instrument.listenToOnce(musician, 'play', function() {
    instrument.playedTimes += 1;
});

musician.trigger('play').trigger('play').trigger('play');

console.log(instrument.playedTimes) // outputs 1

Augmenting objects

Types / prototype based constructor functions can also be augmented with events like so:

function Person(name) {
    this.name = name;
}

mitty(Person.prototype);

var john = new Person('John');

john.on('sayHello', function() {
    console.log(this.name + ' says hello');
});

john.trigger('sayHello'); // outputs 'John says hello'

Installation

Mitty types is packaged as UMD library so you can use it both on client and server (CommonJS and AMD environment) or with browser globals.

// install via npm
npm install mitty --save

// if you use bundler
var mitty = require('mitty');

// or use browser globals
var mitty = window.mitty;