Create an endpoint for a generated JSON site map of every post, page, post-type, etc.

wordpress-json-sitemap.php

<?php

/**
 * Create an endpoint for a generated JSON site map of every post, page, post-type, etc.
 *
 * @return void
 */
function json_sitemap() {
	global $wp;

	$url = 'sitemap.json';

	// Return early if URL is incorrect. Causes 404 in usual cases
	if ( $wp->request !== $url ) {
		return;
	}

	// Setup sitemap variable
	$sitemap = [];

	// Get all posts
	$posts = get_posts([
		'post_type' => 'any',
		'posts_per_page' => -1,
		'post_status' => 'publish'
	]);

	// Get all post urls
	foreach( $posts as $post ) {
		$sitemap[] = get_permalink( $post );
	}

	//Get all post types
	$post_types = get_post_types([
		'public' => true
	]);

	// Get all post type archive urls
	foreach ( $post_types as $post_type) {
		$sitemap[] = get_post_type_archive_link( $post_type );
	}

	// Get all authors
	$authors = get_users();

	// Get all author urls
	foreach ($authors as $author) {
   		$sitemap[] = get_author_posts_url( $author->ID );
	}

	// Get all public taxonomies
	$taxonomies = get_taxonomies([
		'public' => true
	]);

	foreach ( $taxonomies as $taxonomy ) {
		// Get all terms for each taxonomy
		$terms = get_terms([
			'taxonomy' => $taxonomy,
			'hide_empty' => false,
		]);

		// Get all term urls
		foreach( $terms as $term ){
			$sitemap[] = get_term_link( $term );
		}
	}

	// Get the search page
	$sitemap[] = home_url('?s=');

	// Get the search page with no results
	$sitemap[] = home_url('?s=most%20likely%20an%20empty%20search%20result%20page');

	// Get a 404 page
	$sitemap[] = home_url('404-page-most-likely-not-found/');

	// Remove any falsy values
	$sitemap = array_filter($sitemap);

	// Reset array keys
	$sitemap = array_values($sitemap);

	//Send a JSON response back and exit
	wp_send_json($sitemap, 200);
}
add_action( 'template_redirect', 'json_sitemap' );