const map = (func, arr) => {
  const newArr = [];
  for (const el of arr) {
    const newEl = func(el);
    newArr.push(newEl);
  }
  return newArr;
};
console.log(
  map(b => b + 's', ['kestrel', 'kite']),
  map(p => p.age, persons)
);