Write a JavaScript program to get the highest index at which value should be inserted into array in order to maintain its sort order

const sortedLastIndex = (arr, n) => {
  const isDescending = arr[0] > arr[arr.length - 1];
  const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
  return index === -1 ? 0 : arr.length - index;
};

console.log(sortedLastIndex([10, 20, 30, 30, 40], 30));