__proto__.js

var animal = {
  name: 'Animal',
};

var rabbit = {
  type: 'Rabbit',
  __proto__: animal,
};

function RabbitBig() {
  this.size = 'Big';
}

RabbitBig.prototype = rabbit;

var rabbitBig = new RabbitBig();

console.log(animal.name);  // => Animal
console.log(rabbit.name, rabbit.type);  // => Animal Rabbit
console.log(rabbitBig.name, rabbitBig.type, rabbitBig.size); // => Animal Rabbit Big