Example for the Node.js Event Emitter http://blog.ashworth.in/how-to-use-the-node-js-eventemitter/

gistfile1.js

var util = require('util');
var events = require('events');

// Create the object constructor
function Cat(name) {
    this.name = name;
}

// Inherit the EventEmitter
util.inherits(Cat, events.EventEmitter);

// Make the cat meow with a message
Cat.prototype.meow = function(message) {
    this.emit('meow', message);
}

// Create a cat
var kitty = new Cat('Mittens');
kitty.on('meow', function(msg) {
    console.log('We got a message from Mittens:', msg);
});

kitty.meow('Purrrr');