WordPress Function: in_category_extended()

The core WordPress function in_category() is pretty handy but it’s also pretty basic.

in_category_extended() is designed to extend the functionality of in_category() in the following ways:

1. test if the current post is assigned to the specified category OR any descendant categories
2. return TRUE if you are viewing the specified category page OR any descendant category pages

Sure, you can do this a bunch of different ways, using multiple functions and code snippets, but I want a single boolean PHP function to use in my templates.

Example Usage

The main navigation consists of category tabs with on/off states.
If I’m viewing a post OR a category page which is related to the “development” category, then I want to apply a class="current" to the development tab element, which I can then style accordingly with CSS.

class="<?= in_category_extended('development') ? 'current' : '' ?>"

Function Definition

bool in_category_extended($category)

returns TRUE if the current webpage is related to the specified category

Function Parameters

$category
(mixed) (required) Category specified by ID (integer), or slug (string)

Function Code

This function has come in very handy for me – I hope you find it useful too!

function in_category_extended($category) {
 
	// easy out
	if (!(is_category() or is_single())) return false;
 
	// retrieve specified category (ID or slug)
	$obj_specified_category = is_numeric($category) ? get_category($category) : get_category_by_slug($category);
	if (empty($obj_specified_category->cat_ID)) return false;
 
	// we're viewing a category
	if (is_category()) {
		$current_category_ID = get_query_var('cat');
		return ($obj_specified_category->cat_ID == $current_category_ID or cat_is_ancestor_of($obj_specified_category->cat_ID,$current_category_ID));
	}
 
	// we're viewing a post
	else {
		global $wp_query;
		$obj_post = $wp_query->get_queried_object();
		if (empty($obj_post->ID)) return false; 
 
		if (in_category($obj_specified_category->cat_ID, $obj_post->ID)) return true;
		else return in_category(get_term_children($obj_specified_category->cat_ID, 'category'), $obj_post->ID);
	}
}