Why are there no commas in javascript ads?

Question

I am immersed in the new Javascript ES6 classes, and I cannot understand why these class definitions do not use commas, as in object literals.

Example from MDN:

class Polygon {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }

  get area() {
    return this.calcArea();
  }

  calcArea() {
    return this.height * this.width;
  }
}

This is not a real problem, but I feel that something is missing. Thanks for any direction!