text: const sortedLastIndexBy = (arr, n, fn) => {
  const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
  const val = fn(n);
  const index = arr
  .map((val, i) => [i, fn(val)])
  .reverse()
  .findIndex(el => (isDescending ? val <= el[1] : val >= el[1]));
  return index === -1 ? 0 : arr.length - index;
  };
  module.exports = sortedLastIndexBy;