JS Bin

class Rectangle {

  constructor(height, width) {

    this._name = 'Rectangle'

    this._height = height

    this._width = width

  }

  sayName() {

    console.log(`Hi, I am a ${this._name}`)

  }

​

  calculateArea() {

    return this._height * this._width

  }

}

​

class Square extends Rectangle {

  constructor(length) {

    // Here, it calls the parent class's constructor with lengths

    // provided for the Rectangle's width and height

    super(length, length)

​

    // Note: In derived classes, super() must be called before you

    // can use 'this'. Leaving this out will cause a reference error.

    this._name = 'Square'

  }

​

  calculateSurfaceArea() {

    return this.calculateArea() * 6

  }

}

​

const myRectangle = new Rectangle(5, 7)

myRectangle.sayName()

const rectangleArea = myRectangle.calculateArea()

console.log(rectangleArea)

​

console.log('----')

​

const mySquare = new Square(7)

mySquare.sayName()

const squareArea = mySquare.calculateArea()

console.log(squareArea)

​

// call calculateSurfaceArea() method owned by

// the child class (Square)

const surfaceAreaOfSquare = mySquare.calculateSurfaceArea()

console.log(surfaceAreaOfSquare)

​

​

​