registering-scripts.php

<?php

/*
 * Everything registered here will be concatenated into a single script that is 
 * served via /?wp_service_worker=1 which is installed as the service worker.
 */
add_action( 'wp_front_service_worker', function( WP_Service_Workers $sw ) {
	$sw->register_script(
		'static-file',
		plugin_dir_url( __FILE__ ) . 'example.js',
		array( 'main-site-id' ) // Dependency declared so this script will be output after the following.
	);
	
	$sw->register_script(
		'main-site-id',
		function() {
			return sprintf( 'const mainSiteId = %s;', wp_json_encode( get_main_site_id() ) );
		}
	);
} );