EventEmitter.js

function EventEmitter(){}

EventEmitter.prototype.on = function(event, fct){
    this._events = this._events || {};
    this._events[event] = this._events[event]    || [];
    this._events[event].push(fct);
};

EventEmitter.prototype.emit = function(event /* , args... */){
    this._events = this._events || {};
    if( event in this._events === false  )    return;
    for(var i = 0; i < this._events[event].length; i++){
        this._events[event][i].apply(this, Array.prototype.slice.call(arguments, 1));
    }
};