AngularJS directive to open external links in a new tab

external-links.directive.js

(function () {
  'use strict';

  angular
    .module('externalLink', [])
    .directive('a', AFactory);

  function AFactory() {
    return {
      restrict: 'E',
      link: function ($scope, $element, $attrs) {
        $attrs.$observe('href', addTarget);
        $attrs.$observe('ng-href', addTarget);
        
        function addTarget(href) {
          var domainPattern = /^(?:[a-z]{2,30}:)?(?:\/\/)([^:\/?]*)/i,
          domainMatch = domainPattern.exec(href),
          domain, currentDomain;

          if (!domainMatch || domainMatch.length < 2) {
            return;
          }

          domain = domainMatch[1].toLowerCase();
          currentDomain = window.location.hostname.toLowerCase();

          if (domain !== currentDomain) {
            $attrs.$set('target', '_blank');
            // Mark that this directive added the target attribute
            $element.data('externalLink', true);
          } else if ($element.data('externalLink')) {
            $attrs.$set('target', '_self');
          }
        }
      }
    };
  }
}());