kind

class Circle extends Shape {

#Constructor

constructor (radius) {
  this.radius = radius
}

#method

getArea () {
  return Math.PI *2 *this.radius
}

#Call the superclass method

expand(n) {
  return super.expand(n) *Math.PI
}

#Static methods

static createFromDiameter(diameter) {
  return new Circle(diameter /2)
}

Syntactic sugar for prototypes. See: classes