events.js

function Events() {
    var self = this;
 
    self.events = {};
 
    self.on = function(event, callback, context) {
        self.events.hasOwnProperty(event) || (self.events[event] = []);
        self.events[event].push([callback, context]);
    };
 
    self.emit = function(event) {
        var tail = Array.prototype.slice.call(arguments, 1),
            callbacks = self.events[event];
 
        if (callbacks) {
            for (var i = 0, l = callbacks.length; i < l; i++) {
                var callback = callbacks[i][0],
                    context = callbacks[i][1] === undefined ? self : callbacks[i][1];
                callback.apply(context, tail);
            }
        }
    };
    
    self.off = function(event, callback) {
        self.events[event] = self.events[event].filter(function(x){
            return x[0] !== callback;
        })
    }
}