That's because the child constructor must call `super()`. Here's the corrected code: ```js run class Animal { constructor(name) { this.name = name; } } class Rabbit extends Animal { constructor(name) { *!* super(name); */!* this.created = Date.now(); } } *!* let rabbit = new Rabbit("White Rabbit"); // ok now */!* alert(rabbit.name); // White Rabbit ```