How to add rel="nofollow" to all external links that do not related to my domain with javascript?

Question

I have the following html string with three links:

var html = '
   <a href="http://www.example.com/help">Go to help page</a>
   <a href="http://blog.example.com">Go to blog page</a>
   <a href="https://google.com">Go google</a>
';

My domain name is example.com. As you can see from the code above there is two internal links and one external.

I need to write "magic" function that adds rel="nofollow" attribute to all external links (not internal ones). So I need to get the following result:

var html = '
   <a href="http://www.example.com/help">Go to help page</a>
   <a href="http://blog.example.com">Go to blog page</a>
   <a href="https://google.com" rel="nofollow">Go google</a>
';

I'm trying to write that function and this is I have at the time:

function addNoFollowsToExternal(html) {
  // List of allowed domains
  var whiteList = ['example.com', 'blog.example.com'];

  // Regular expression
  var str = '(<a\s*(?!.*\brel=)[^>]*)(href="/https?://)((?!(?:(?:www\.)?' + whiteList.join(',') + '))[^"]+)"((?!.*\brel=)[^>]*)(?:[^>]*)>',

  // execute regexp and return result
  return html.replace(new RegExp(str, 'igm'), '$1$2$3"$4 rel="nofollow">');
}

Unfortunately my regexp seems does't work. After executing addNoFollowsToExternal(html) rel="nofollow" don't added to external link with href="https://google.com"

Please help me with fixing my regular expression to resolve my task.

Anubis · Accepted Answer · 2016-06-20T08:17:38.227

6

There were some minor mistakes in your RegEx. Here is a corrected version:

function addNoFollowsToExternal(html){
    var whiteList = ['([^/]+\.)?example.com'];
    var str = '(<a\s*(?!.*\brel=)[^>]*)(href="https?://)((?!(?:' + whiteList.join('|') + '))[^"]+)"((?!.*\brel=)[^>]*)(?:[^>]*)>';

    return html.replace(new RegExp(str, 'igm'), '$1$2$3"$4 rel="nofollow">');
}

edited Jun 20 '16 at 08:17

answered Jun 16 '16 at 15:27

Anubis

481
4
4

Thanks for the help. Is it possible to don't list all subdomains in `whiteList` array but just use `*.example.com` for example? – Erik Jun 16 '16 at 15:42
I modified the above function to your needs by removing the www. part from the regex and adding some tweaks to your whitelist – Anubis Jun 20 '16 at 08:18
Thanks. Is this robust solution? Is it possible to hack it somehow? I'm asking becasue planing to use it n production – Erik Jun 20 '16 at 08:43
How to modify your regexp to check port also, so to be possible check agains such whitelist `['([^/]+\.)?example.com:8080']` ? – Erik Jun 22 '16 at 08:09

score 0 · Answer 2 · answered Jul 07 '18 at 21:33

you can also use function below

private function _txt2link($text){

         $regex = '/'
          . '(?<!\S)'
          . '(((ftp|https?)?:?)\/\/|www\.)'
          . '(\S+?)'
          . '(?=$|\s|[,]|\.\W|\.$)'
          . '/m';

        return preg_replace_callback($regex, function($match)
        {
            return '<a'
              . ' target="_blank"'
              . ' rel="nofollow"'
              . ' href="' . $match[0] . '">'
              . $match[0]
              . '</a><br/>';
        }, $text);
    }

How to add rel="nofollow" to all external links that do not related to my domain with javascript?

2 Answers2