box.ts

class Box {
  width: number;
  height: number;
  constructor(width: number, height: number) {
    this.width = width;
    this.height = height;
  }
  get area() { return this.width*this.height; }
  setSquare(side: number) {
    this.width = this.height = side;
  }
  static ZeroSize() { return new Box(0, 0); }
}