extends

class ChildClass extends ParentClass { ... }

class Square extends Polygon {
  constructor(length) {
    // Here, it calls the parent class' constructor with lengths
    // provided for the Polygon's width and height
    super(length, length
    // Note: In derived classes, super() must be called before you
    // can use 'this'. Leaving this out will cause a reference error.
    this.name = 'Square';
  }

  get area() {
    return this.height * this.width;
  }
}

class myDate extends Date {
  constructor() {
    super(
  }

  getFormattedDate() {
    var months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
    return this.getDate() + '-' + months[this.getMonth()] + '-' + this.getFullYear(
  }
}

class nullExtends extends null {
  constructor() {}
}

Object.getPrototypeOf(nullExtends // Function.prototype
Object.getPrototypeOf(nullExtends.prototype) // null

new nullExtends( //ReferenceError: this is not defined