Shape2.ts

const getArea = (shape: Shape) => {
  if (shape.radius) {
    return Math.PI * Math.pow(shape.radius, 2)
  } 
  else if (shape.height && shape.width) {
    return shape.height * shape.width
  } 
  else if (shape.base && shape.height) {
    return 0.5 * shape.base * shape.height
  } 
  else {
    throw new Error('Invalid shape')
  }
}