class Animal {

    constructor (name, fly=false, sound) {

        this.name = name

        this.fly = fly

        this.sound = sound

    }

    canFly (fly) {

      if(this.fly) {

        return 'goes up up in the sky'

      }

      return 'stays on the ground'

    }

    talk (sound) {

      return this.sound;

    }

    describe () {

console.log(`${this.name}

${this.canFly()}

and shouts '${this.talk()}'`)

    }

}

​

class Cat extends Animal {

    constructor() {

        super()

        this.name = 'cat'

        this.fly = false

        this.sound = 'miao'

    }

}

​

class Bird extends Animal {

    constructor() {

        super()

        this.name = 'bird'

        this.fly = true

        this.sound = 'tchirp'

    }

}

​

​

var bird = new Bird()

var cat  = new Cat()

​

bird.describe()

cat.describe()

​