Open all external links (different hostname than current page) in new tab/window with plain vanilla JavaScript.

target_blank--external.js

/**
* Open external links in new tab/window
*/

// All http:// links should open in new tab/window. Internal links are relative.
var anchors = document.querySelectorAll('a');

for (var i = 0; i < anchors.length; i++) {
	if (anchors[i].host !== window.location.hostname) {
		anchors[i].setAttribute('target', '_blank');
 	}
}

I've tested the codepen version, but it's not working correctly. I'm using it in an XML template in the following form.

<script type='text/javascript'>
/*<![CDATA[*/
function makeExternal(link) {
  var url      = link.getAttribute('href'),
  host         = window.location.hostname.toLowerCase(),
  regex        = new RegExp('^(?:(?:f|ht)tp(?:s)?\:)?//(?:[^\@]+\@)?([^:/]+)', 'im'),
  match        = url.match(regex),
  domain       = ((match ? match[1].toString() : ((url.indexOf(':') < 0) ? host : ''))).toLowerCase();

  // Same domain
  if (domain != host) {    
    link.setAttribute('target', '_blank');    
  }
}

for (var l = 0, links = document.querySelectorAll('a'), ll = links.length; l < ll; ++l ){
   makeExternal(links[l]); 
} 
/*]]>*/
</script>