Frozen Proxies

sample.js

var immutable = (function(){
  function isFunction(f) {
    var getType = {};
    return f && getType.toString.call(f) === '[object Function]';
  }

  function shallowCopy(object){
    var copy = Object.create(Object.getPrototypeOf(object));

    Object.getOwnPropertyNames(object).forEach(function (name){
      copy[name] = object[name];
    });

    return copy;
  }

  return function immutable(object){
    var proxy = new Proxy(object, {
      get: function(target, originalName){
        if (originalName.indexOf('with') === 0 && originalName.length > 4)
        {
          var capitalizedName = originalName.substring(4);
          var name = capitalizedName.charAt(0).toLowerCase() + capitalizedName.slice(1);
          var attribute = target[name];
          if (!attribute || !isFunction(attribute)){
            return function(value){
              var copy = shallowCopy(object);
              copy[name] = value;
              return immutable(copy);
            };
          }
        }

        return target[originalName];
      }
    });

    Object.freeze(object);

    return proxy;
  };
})();

function Vehicle(hasEngine, hasWheels) {
    this.hasEngine = hasEngine || false;
    this.hasWheels = hasWheels || false;
};

function Car (make, model, hp) {
    this.hp = hp;
    this.make = make;
    this.model = model;
};

Car.prototype = new Vehicle(true, true);

var car = immutable(new Car('Hyundai', 'Elantra',  10));

console.log(car.hp);
console.log(car.make);
console.log(car.model);
console.log(car.hasEngine);
console.log(car.hasWheels);
console.log(car.hasMirrors);

var car2 = car.withHp(car.hp + 20).withHasMirrors(true);

console.log(car2.hp);
console.log(car2.make);
console.log(car2.model);
console.log(car2.hasEngine);
console.log(car2.hasWheels);
console.log(car2.hasMirrors);