Nodejs: understanding Events and Emitters

emitter.js

// emitter.js
// returns a Function Constructor
function Emitter () {
    this.events = {}
}

// Listener is the code that responds to an event
// analogy: a person taking a cue from an event to execute his task
// @type : type of event. Ie, onClick
// @listener: code to be executed
Emitter.prototype.on = function (type, listener) {
    this.events[type] = this.events[type] || []
    this.events[type].push(listener)
}

Emitter.prototype.emit = function (type) {
    if (this.events[type]) {
        this.events[type].forEach(function (listener) {
            listener()
        })
    }
}

module.exports = Emitter

index.js

var Emitter = require('./emitter')

var emtr = new Emitter()

emtr.on('greet', function fn1 () {
    console.log('Somewhere, someone says hello!')
})

emtr.on('greet', function fn2 () {
    console.log('A greeting occurred!')
})

console.log('hello!')
emtr.emit('greet')

/*
 * emtr.events = {
 *  greet: [ fn1, fn2 ]
 * }
 */