Add target="_blank" to external links with pure JavaScript. in WordPRess

target_blank.php

add_action( 'wp_footer', function () { ?>
<script>
  document.addEventListener("DOMContentLoaded", function () {
    // remove subdomain of current site's url and setup regex
    var internal = location.host.replace("www.", "");
    internal = new RegExp(internal, "i");

    var a = document.getElementsByTagName("a"); // then, grab every link on the page
    for (var i = 0; i < a.length; i++) {
      var href = a[i].host; // set the host of each link
      if (!internal.test(href)) {
        // make sure the href doesn't contain current site's host
        a[i].setAttribute("target", "_blank"); // if it doesn't, set attributes
      }
    }
     console.log('EJ Loaded page');
  });
</script>

<?php } );