Меню

const user = {
  firstName: `Андрей`,
  lastName: `Зюзин`,
  [Symbol.iterator]() {
        let index = -1;
        const keys = Object.keys(this);
        return {
            next: () => {
                index++;
                return {
                    done: (index >= keys.length),
                    value: this[keys[index]],
                    key: keys[index]
                }
            }            
        };
    }
}

for (value of user) {
  console.log(value);
}