WordPress 5 Plugin: WH_Hello_World

## listing-18-1.php
<?php
/**
 * @package WH_Hello_World
 * @version 1.0.0
 */
/*
Plugin Name: WH Hello World
Plugin URI: https://wordpress-handbuch.com
Description: Testausgabe in Front- und Backend
Author: Richard Eisenmenger
Version: 1.0.0
Author URI: https://richard-eisenmenger.com
*/

function hello_world() {
	echo "<script>alert('Hallo Welt!');</script>\n";
}

add_action( 'admin_head', 'hello_world' );
add_action( 'wp_head', 'hello_world' );