polymorphism.js

class Person {
  constructor (firstName, lastName, birthday) {
    this.firstName = firstName
    this.lastName = lastName
    this.birthday = birthday
  }
  sayHello () {
    return `My name is ${this.firstName}`
  }
}

class SuperGirl extends Person {
  constructor (firstName, lastName, birthday, superpowers) {
    super(firstName, lastName, birthday)
    this.gender = 'female'
    this.superpowers = superpowers
  }
  sayHello () {
    return `
My name is ${this.firstName} ${this.lastName}. Years ago, my planet, Krypton, was in serious peril.
My cousin, Kal-El, was sent to a planet called Earth for his own safety and protection.
You may know his story. The story you don't know is that I was sent to protect him.
`
  }
  fly () {
    return 'I can fly'
  }
}

const sg = new SuperGirl('Kara', 'Zor-El', 1554143709, [
  'flying', 'heat vision', 'strength'
])
console.log(sg.sayHello())