Solution to http://www.codewars.com/kata/52d3b68215be7c2d5300022f/train

solution.js

function Event() {
  this.listeners = [];
}
Event.prototype.subscribe = function(fn) {
  this.listeners.push(fn);
}
Event.prototype.unsubscribe = function(fn) {
  for (var i = 0; i < this.listeners.length; i++) {
    if (this.listeners[i] === fn) {
      this.listeners.splice(i, 1);
    }
  }
}
Event.prototype.emit = function() {
  for (var i = 0; i < this.listeners.length; i++) {
    this.listeners[i].apply(this, arguments);
  }
}