Inheritance

Inheritance is a way to create parent-child relationships between classes. The child class (sometimes referred to as a subclass) has access to the behavior and data defined by the parent class (sometimes referred to as a superclass).

class Pet {
  constructor(name) {
    this.name = name;
  }

  introduce() {
    console.log(`This is my pet, ${this.name}.`);
  }
}

class Dog extends Pet {}

const dog = new Dog('Otis');
dog.introduce();
// => This is my pet, Otis.

The extends keyword in the child class declaration establishes a relationship with the parent class through the prototype chain.

Objects created by the child's constructor will have the parent class's prototype in their prototype chain, providing access to any methods or data defined by the parent.

const dog = new Dog('Otis');

Dog.prototype.isPrototypeOf(dog); // => true
Pet.prototype.isPrototypeOf(dog); // => true
Pet.prototype.isPrototypeOf(Dog.prototype); // => true

Pet.prototype.hasOwnProperty('introduce'); // => true
Dog.prototype.hasOwnProperty('introduce'); // => false
dog.hasOwnProperty('introduce'); // => false

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References

• https://javascript.info/class-inheritance
• https://exercism.org/tracks/javascript/concepts/inheritance
• https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects/Inheritance
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain