test.js

angular.module('test', ['ngSanitize'])
.filter('addTargetBlank', function(){
  return function(x) {      
    var tree = angular.element('<div>'+x+'</div>');
    
    for(var i=0;i < tree.find('a').length;i++){
        if (tree.find('a')[i].href.indexOf(window.location.hostname) == -1) {
            tree.find('a')[i].setAttribute('target', '_blank');
        }
    }

    return angular.element('<div>').append(tree).html(); 
  }
})