Dependency Inversion Principle

dip.js

class Ingredient {
  // implementation
}

class Milk extends Ingredient {
  // implementation
}

class Beverage {
  constructor(ingredient) {
    this.ingredient = ingredient
  }

  cost() {
    // calculate the cost
  }
}

class Coffee extends Beverage {
  cost() {
    // calculate the cost
  }
}