Model base class. Features inheritance, automatically created accessors (get + set) and encapsulation of data. Setters are chainable.

model.js

var Model = function(attrs)
{
    this.attrs = attrs;

    for (var attr in attrs)
        var tmp = function(name) {
            this[attr] = function(x) {
                if (arguments.length) {
                    this.attrs[name] = x;
                    return this;
                }
                return this.attrs[name];
            }.bind(this);
        }.bind(this)(attr);
};

Model.extend = function(extras, model)
{
    if (2 > arguments.length)
        model = Model;
    
    var obj = function(attrs) {
        model.call(this, attrs);
        
        if (extras && extras.initialize)
            extras.initialize.call(this, attrs);
    };

    obj.prototype = Object.create(model.prototype);
    return obj;
}

var Car = Model.extend({
    initialize: function(attrs) {
        this.wheels = 'fast';
    }
});

var FastCar = Model.extend({}, Car);     

var myCar     = new Car({ color: 'blue', year: 1999, make: 'Skoda' }); 
var myFastCar = new FastCar({ color: 'baby-blue', year: 1969, make: 'Fiat' });

console.log('myCar before upgrade: ', myCar.color(), myCar.make() , myCar.year());            

// Upgrade!
myCar
    .year(2009)
    .color('yellow')
    .make('Ferrari');

console.log('myCar after upgrade: ', myCar.color(), myCar.make() , myCar.year());   
console.log('fastCar: ', myFastCar.color(), myFastCar.make(), myFastCar.year(), myFastCar.wheels);