is_child() function

Question

My need is to check if a page is subpage of a page (with ID).

I try to get this code working but it doesn't.

function is_child($pageID) {
  global $post;
  echo $post->post_parent; // display the right ID!
  if( is_page() && $post->post_parent == $pageID ) {
    return true;
  } else {
    return false;
  }
}

It returns always false while $post->post_parent returns the right ID!

Testing code (which always returns no while $post->$post_parent echoes the good ID in the function):

if(is_child(2310)) {
    echo 'yes';
} else {
    echo 'no';
}

This function takes place in my functions.php file and its purpose is to load CSS through a condition statement (load a particular CSS file if page is X or child of X).

This code can be found on many sites around there but was produced in 2012-2013.

Thanks a lot for any help.

Sources of unworking codes : https://bavotasan.com/2011/is_child-conditional-function-for-wordpress/ https://www.kevinleary.net/wordpress-is_child-for-advanced-navigation/

Answer 1

/**
 * Return whether the current page is a child of $id
 *
 * Note: this function must be run after the `wp` hook.
 * Otherwise, the WP_Post object is not set up, and
 * is_page() will return false.
 *
 * @param  int  $id The post ID of the parent page
 * @return bool     Whether the current page is a child page of $id
 */
function is_child_of( $id ) {
  return ( is_page() && $id === get_post()->post_parent );
}

Answer 2

So I did this and it works. But @NathanJohnson answer is nicer.

function is_child($pageID) {
  $parentID = wp_get_post_parent_id(get_the_ID());
  if( is_page() && $parentID == $pageID ) {
    return true;
  } else {
    return false;
  }
}