observable.js

(function(global){

    'use strict';

    var O = function O(defaults){
        defaults.__proto__ = this;
        this._listeners = {};
        return defaults;
    }

    O.prototype.get = function get(name){
        return this[name];
    };

    O.prototype.set = function set(name, value){
        var previous = this[name];
        this[name] = value;
        if (this._listeners[name]){
            this._listeners[name].call(this, {value: value, previous: previous, name: name});
        }
    };

    O.prototype.on = function on(name, listener){
        this._listeners[name] = listener;
    };

    global.O = O;

})(this);


// TESTs
var obj = new this.O({one: 1, two: 2, three: 3});
console.log(obj.get('one') === 1);
console.log(obj.one === 1);
obj.on('two', function(evt){ console.log( evt.value === 'too'); });
obj.set('two', 'too');