WordPress plugin to open external links in a new tab in the WordPress admin

admin-links-new-tab.php

<?php
/**
 * Plugin Name: Open Admin Links in New Tab
 * Author: Mark Jaquith
 */

add_action('admin_footer', function () {
echo <<<SCRIPT
	<script>
		document.body.addEventListener('click', (e) => {
			const a = e.target.closest('a');
			if (a && !a.href.includes('#')) {
				const url = new URL(a.href);
				const domain = url.hostname;
				if (document.domain !== domain && !a.target) {
					a.target = '_blank';
				}
			}
		});
	</script>
SCRIPT;
});