JavaScript Design Patterns - Structural - Facade

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The facade pattern provides a simplified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem more straightforward to use.

In the below example, we are creating a simple interface Cart that abstracts all the complexity from several subsystems such as Discount, Shipping, and Fees:

class Cart {
  constructor() {
    this.discount = new Discount();
    this.shipping = new Shipping();
    this.fees = new Fees();
  }

  calc(price) {
    price = this.discount.calc(price);
    price = this.fees.calc(price);
    price += this.shipping.calc();

    return price;
  }
}

class Discount {
  calc(value) {
    return value * 0.85;
  }
}

class Shipping {
  calc() {
    return 500;
  }
}

class Fees {
  calc(value) {
    return value * 1.1;
  }
}