function Sale(price) {
  this.price = price || 100;
}
Sale.prototype.getPrice = function () {
  return this.price;
};

Sale.decorators = {}; // 装饰器

Sale.decorators.fedtax = {
  getPrice: function () {
    var price = this.uber.getPrice();
    price += price * 5 / 100;
    return price;
  }
};

Sale.decorators.quebec = {
  getPrice: function () {
    var price = this.uber.getPrice();
    price += price * 7.5 / 100;
    return price;
  }
};

Sale.prototype.decorate = function (decorator) {
  var F = function () {},
      overrides = this.constructor.decorators[decorator],
      i, newobj;
  F.prototype = this;
  newobj = new F();
  newobj.uber = F.prototype;
  for ( i in overrides) {
    if (overrides.hasOwnProperty(i)) {
      newobj[i] = overrides[i];
    }
  }
  return newobj;
};

var sale = new Sale();
console.log(sale.getPrice());   // 100
sale = sale.decorate('fedtax');
console.log('after fedtax:' + sale.getPrice()); //after fedtax: 105