19. Working with JavaScript Subclasses

Working with subclasses

Like most of the new additions, there's a lot less setup code and it's a lot cleaner syntax to create a subclass using class, super, and extends.

Just remember that, under the hood, the same connections are made between functions and prototypes.

super must be called before this

In a subclass constructor function, before this can be used, a call to the super class must be made.

class Apple {}
class GrannySmith extends Apple {
  constructor(tartnessLevel, energy) {
    this.tartnessLevel = tartnessLevel; // `this` before `super` will throw an error!
    super(energy); 
  }
}