wordpress check if is page or subpage of that page

is_page.php

<?php

$is_page = function($pages) {
  global $post;
  if (!is_page()) return false;
  if (is_page($pages)) return true;
  if (empty($post->post_parent)) return false;
  $parent = get_post($post->post_parent);
  if (!$parent || empty($parent->post_name)) return false;
  $slug = $parent->post_name;
  foreach ((array) $pages as $page) if ($slug === $page) return true;
  return false;
};

$is_page('events') matches /events/**

based on Testing_for_sub-Pages