class

class Polygon {
  constructor(height, width) {
    this.area = height * width;
  }
}
console.log(new Polygon(4, 3).area);
// Expected output: 12

class name [extends otherName] {
  // クラス本体
}

class Rectangle {
  constructor(height, width) {
    this.name = "Rectangle";
    this.height = height;
    this.width = width;
  }
}
class FilledRectangle extends Rectangle {
  constructor(height, width, color) {
    super(height, width);
    this.name = "Filled rectangle";
    this.color = color;
  }
}

class Foo {}
class Foo {} // Uncaught SyntaxError: Identifier 'Foo' has already been declared

let Foo = class {};
class Foo {} // Uncaught SyntaxError: Identifier 'Foo' has already been declared