[javascript patterns] Decorator.

gistfile1.js

var Sale = function (price) {
  this.price = price > 0 ? price : 100;
  this.decorators_list = [];
};

Sale.decorators = {};

Sale.decorators.fedtax = {
  getPrice: function (price) {
    return price + price * 0.05;
  }
};

Sale.decorators.quebec = {
  getPrice: function (price) {
    return price + price * 0.075;
  }
};

Sale.decorators.money = {
  getPrice: function (price) {
    return "$" + price.toFixed(2);
  }
};

Sale.prototype.decorate = function (decorator) {
  this.decorators_list.push(decorator);
};

Sale.prototype.getPrice = function () {
  var price = this.price,
      i,
      max = this.decorators_list.length,
      name;
  for (i = 0; i < max; i += 1) {
    name = this.decorators_list[i];
    price = Sale.decorators[name].getPrice(price);
  }
  return price;
};

// usage
var iPhone = new Sale(100);
iPhone.decorate('quebec');
iPhone.decorate('fedtax');
iPhone.decorate('money');
console.log(iPhone.getPrice());