Discussion on: How to Get the Intersection of Two Arrays

The Set solution is not equivalent due to the filtered result being put through another Set, eliminating duplicates, while the plain filter+includes solution will return duplicates from the first array.

The indexOf solution shouldn't (ab)use an object as a hash map, and then parseInt, really, pretty please. People might copy that code, especially as it is last in your article.

My general purpose solution would be:

/**
 * Return elements present in both arrays, without duplicates
 */
function intersectWith(arr, other) {
  const known = new Set(arr);
  return other.filter(function(e) {
    if (!known.has(e)) {
      return false;
    }
    known.delete(e); // Avoid duplicates. Remove line if you want duplicates from other.
    return true;
  });
}

I like to avoid the conversation from array to another array (with filter) to a Set and back to array again 😁