get_the_category( int $post_id = false )

function get_the_category( $id = false ) {
	$categories = get_the_terms( $id, 'category' );
	if ( ! $categories || is_wp_error( $categories ) )
		$categories = array();

	$categories = array_values( $categories );

	foreach ( array_keys( $categories ) as $key ) {
		_make_cat_compat( $categories[$key] );
	}

	/**
	 * Filters the array of categories to return for a post.
	 *
	 * @since WP-3.1.0
	 * @since WP-4.4.0 Added `$id` parameter.
	 *
	 * @param array $categories An array of categories to return for the post.
	 * @param int   $id         ID of the post.
	 */
	return apply_filters( 'get_the_categories', $categories, $id );
}