cas

const intersectionUnion = (arr1, arr2) => {
  let sharedAll = arr1
    .concat(arr2)
    .filter((x) => arr1.includes(x) && arr2.includes(x));

  let intersection = [...new Set(sharedAll)].sort();
  let union = [...new Set(arr1.concat(arr2))].sort();

  return [intersection, union];
};

console.log(intersectionUnion([1, 2, 3, 4, 4], [4, 5, 9])); // [[4], [1, 2, 3, 4, 5, 9]]
console.log(intersectionUnion([1, 2, 3], [4, 5, 6])); // [[], [1, 2, 3, 4, 5, 6]]