How to apply nofollow and target_blank on external links in text created with CKEditor?

When I create a node, I often need to add links to external websites in the text.

I want all the external links to open in a new tab and I want them to have a nofollow.

The body field uses CKEditor.

How do I apply nofollow and target_blank on external links in text created with CKEditor?

You can do this automatically by creating your own text filter in a custom module.

Note that the /** @Filter ... */ in front of the class is not a comment, but an annotation, it has to be included in the file. Replace all fancy uppercase stuff with your own code.

src/Plugin/Filter/MYFANCYFILTER.php

<?php

namespace Drupal\MY_MODULE\Plugin\Filter;

use Drupal\filter\FilterProcessResult;
use Drupal\filter\Plugin\FilterBase;
use Drupal\Component\Utility\Html;

/**
 * @Filter(
 *   id = "MY_FANCY_FILTER",
 *   title = @Translation("My fancy filter"),
 *   description = @Translation("Makes HTML even more fancier"),
 *   type = Drupal\filter\Plugin\FilterInterface::TYPE_TRANSFORM_REVERSIBLE
 * )
 */
class MYFANCYFILTER extends FilterBase {

  public function process($text, $langcode) {
    $result = new FilterProcessResult($text);
    $dom = Html::load($text);
    $xpath = new \DOMXPath($dom);

    // to select all links you have to create a XPath query 
    // the example query below selects all <a> tags which have a "href" attribute
    // see https://www.w3schools.com/xml/xpath_syntax.asp
    foreach ($xpath->query("//a[@href]") as $element) {
      // the example logic below accepts all links starting with "http://" or "https://" or "//"
      if (preg_match('|^(https?:)?//.+|', $element->getAttribute('href')) === 1) {
        // see https://www.php.net/manual/de/class.domelement.php
        // for docs about manipulating HTML markup
        $element->setAttribute('MY_ATTRIBUTE', 'MY_VALUE');
      }
    }
    $result->setProcessedText(Html::serialize($dom));
    return $result;
  }
}

Then enable your new text filter for the corresponding text format in
Configuration > Content authoring > Text formats and editors

I have tried to add target="_blank" by using Text Format=Full HTML using Source button.

It worked for me.

If you do not want manually then you can try following module https://www.drupal.org/project/editor_advanced_link