README.md

Decorator Pattern

The Decorator pattern allows behavior to be added to individual objects, dynamically, without affecting the behavior of other objects from the same class.

Example

// Base component
class Coffee {
  cost() {
    return 5;
  }
}

// Decorator base class
class CoffeeDecorator {
  constructor(coffee) {
    this.coffee = coffee;
  }

  cost() {
    return this.coffee.cost();
  }
}

// Concrete Decorators
class MilkDecorator extends CoffeeDecorator {
  cost() {
    return this.coffee.cost() + 1;
  }
}

class SugarDecorator extends CoffeeDecorator {
  cost() {
    return this.coffee.cost() + 0.5;
  }
}

Explaining the code

1. Base Component: The Coffee class represents the base component with a cost method that returns the base price of a coffee, which is 5.

2. Decorator Base Class: The CoffeeDecorator class is a base decorator class that takes a coffee object and delegates the cost method to it. This class is designed to be extended by concrete decorators.

3. Concrete Decorators:

   • MilkDecorator
     • The MilkDecorator class extends CoffeeDecorator and adds the cost of milk (1) to the base coffee cost.
   • SugarDecorator
     • The SugarDecorator class extends CoffeeDecorator and adds the cost of sugar (0.5) to the base coffee cost.

Usage

let myCoffee = new Coffee();
console.log(myCoffee.cost()); // 5

myCoffee = new MilkDecorator(myCoffee);
console.log(myCoffee.cost()); // 6

myCoffee = new SugarDecorator(myCoffee);
console.log(myCoffee.cost()); // 6.5

• Initially, myCoffee is a plain Coffee object with a cost of 5.
• Then, myCoffee is wrapped with a MilkDecorator, increasing the cost to 6.
• Finally, myCoffee is wrapped with a SugarDecorator, increasing the cost to 6.5.

Summary

The Decorator pattern is used to dynamically add additional costs (milk and sugar) to a base coffee object. This pattern is useful for extending the functionality of objects in a flexible and reusable way.