box.js

class Box {
  constructor(width, height) {                  // initializer
    this.width = width;
    this.height = height;
  }
  get area() { return this.width*this.height; } // getter function
  setSquare(side) {                             // normal function
    // set the Box's width and height to side, representing a square
    this.width = this.height = side;
  }
  static ZeroSize() { return new Box(0, 0); }   // static (class-level) function
}
var big = new Box(1920, 1080);
var mini = new Box(19.2, 10.8);
console.log(`The big box is ${big.area/mini.area} times larger than the minibox`);
console.log(`The area of the zero-size box is ${Box.ZeroSize().area}.`);