decorator.js

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

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

Sale.prototype.decorate = function(decorator) {
	var overrides = this.constructor.decorators[decorator],
	newobj,
	i;

	newobj = Object.create(this);
	newobj.uber = this;

	for(i in overrides) {
		newobj[i] = overrides[i];
	}
	return newobj;
};

Sale.decorators = {};

Sale.decorators.fedtax = {
	getPrice: function() {
		var price = this.uber.getPrice();
		price += 1;
		return price;
	}
}

var sale = new Sale();
sale = sale.decorate('fedtax');