class

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

console.log(new Polygon(4, 3).area);
// Expected output: 12

    class name [extends] {
      // class body
    }

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

class Square extends Polygon {
  constructor(length) {
    super(length, length);
    this.name = "Square";
  }
}

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

var Foo = class {};
class Foo {} // Uncaught TypeError: Identifier 'Foo' has already been declared