class Box {
  constructor (width, length, height, weight) {
	this._width  = width;
	this._length = length;
	this._height = height;
	this._weight = weight;
  }

  get width () {
	  return this._width;
  }
  set width (width) {
	  this._width = width;
  }
  get length () {
	  return this._length;
  }
  set length(length) {
	  this._length = length;
  }
  get height () {
	  return this._height;
  }
  set height(height) {
	  this._height = height;
  }
  get volume() {
	 return this.width * this.length * this.height;
  }
}

var shoeBox = new Box(20, 35, 15, 0.2);
console.log('current volume: '+shoeBox.volume);
shoeBox.lenth = 15;
shoeBox.width = shoeBox.height * 0.5;
console.log('new volume: '+shoeBox.volume);
console.log(shoeBox);