addTargetToLink.js

/*
  外部サイトへのリンクに「rel="external nofollow" target="_blank"」を付ける
  ※prototype.jsが必要
*/

var addRelToLink = function(target) {
  var host = new RegExp(location.host);
  var js = /^javascript\:/;
  Selector.findChildElements(target, ['a']).each(function(link) {
    if (!host.test(link) && !js.test(link)) {
      link.rel = 'external nofollow';
    };
  });
};

var addTargetToLink = function(target) {
  Selector.findChildElements(target, ['a']).each(function(link) {
    if (link.rel == 'external nofollow' ||
        link.rel == 'nofollow external' ||
        link.rel == 'external')
    {
      link.target = '_blank';
    } else {
      link.target = '_self';
    };
  });
};

document.observe('dom:loaded', function(event) {
  addRelToLink(document);
  addTargetToLink(document);
}, false);

document.observe('DOMNodeInserted', function(event) {
  var target = event.target;
  addRelToLink(target);
  addTargetToLink(target);
}, false);