decorator_classic_oop_pattern_part_2.1.js

/**
 * Base decorator for Coffee ingredients
 * @param target
 * @param cost
 * @returns {any}
 */
function baseCoffeeIngredientDecorator(target, cost) {
	// save a reference to the original constructor
	var original = target;

	// a utility function to generate instances of a class
	function construct(constructor, args) {
		const c :any = function () {
			return constructor.apply(this, args);
		};

		c.prototype = constructor.prototype;

		let ret = new c();
		ret.cost += cost;
		return ret;
	}

	// the new constructor behaviour
	const f :any = function (...args) {
		return construct(original, args);
	};

	// copy prototype so intanceof operator still works
	f.prototype = original.prototype;

	// return new constructor (will override original)
	return f;
}

/**
 * Decorator A
 */
function withMilk(target) { return baseCoffeeIngredientDecorator(target, 0.5) }

/**
 * Decorator B
 */
function withWhip(target) { return baseCoffeeIngredientDecorator(target, 0.7) }

/**
 * Decorator C
 */
function withSprinkles(target) { return baseCoffeeIngredientDecorator(target, 0.2) }


/**
 * ConcreteComponent
 * (class for decorate)
 */
@withMilk
@withWhip
@withSprinkles
class Coffee {
	private cost :number = 1;

	getCost() :number {
		return this.cost;
	}
}

var myCoffee = new Coffee();
console.log(myCoffee.getCost());