odin-default-js-exercises/findTheOldest/findTheOldest.js

const findTheOldest = function(array) {
  return array.reduce((oldest, currentPerson) => {
    const oldestAge = getAge(oldest.yearOfBirth, oldest.yearOfDeath);
    const currentAge = getAge(currentPerson.yearOfBirth, currentPerson.yearOfDeath);
    return oldestAge < currentAge ? currentPerson : oldest;
  })
};

const getAge = function(birth, death) {
  if (!death) {
    death = new Date().getFullYear();
  }
  return death - birth;
};

module.exports = findTheOldest;