Custom twig function and filter - Drupal

Twig is a part of the Symfony framework and was introduced as a template engine. Drupal 8 also uses twig as a template engine.

We can modify incoming data to twig using Drupal 8 template hooks but we also need some quick filter and dynamic functions that we can directly inject into a particular template.

Drupal 8 provides a way to create a custom twig extension, Let’s see how we can do this

1. Declare your custom module using the info.yml file. Here our example module name is “Twig Extension” (twig_extension). [file name:- twig_extension.info.yml]

   name: Twig Extension
   type: module
   description: 'Twig custom extension - Filter and function'
   package: Theme
   core: 8.x

2. Now declare a twig extension service as below. [file name:-twig_extension.services.yml]

   services:
     twig_extension.function:
       class: Drupal\twig_extension\TwigExtension\TwigFunctionExtension
       tags:
         - { name: twig.extension }
     twig_extension.filter:
       arguments: ['@renderer']
       class: Drupal\twig_extension\TwigExtension\TwigFilterExtension
       tags:
         - { name: twig.extension }

   Make sure to use service tag twig.extension, This will tell Drupal 8 that this service is for twig extension.
3. Create a twig filter using Twig_SimpleFilter class. [file name:-TwigFilterExtension.php]

   <?php
   namespace Drupal\twig_extension\TwigExtension;
   /**
    * Class TwigFilterExtension.
    */
   class TwigFilterExtension extends \Twig_Extension{
     /**
      * Declare your custom twig filter here
      *
      * @return array|\Twig_SimpleFilter[]
      */
     public function getFilters()
     {
       return [ 
         new \Twig_SimpleFilter(
           'remove_links', 
           array($this, 'removeLinks')
         )
       ];
     }
     /**
      * Function to remove only links from the html
      * @param $string
      *  Html as string
      *
      * @return string
      *  Filtered html
      */
     public static function removeLinks($string)
     {
       return preg_replace('#<a.*?>(.*?)</a>#i',
         '\1',
         $string);
     }
     /**
      * {@inheritdoc}
      * @return string
      */
     public function getName()
     {
       return 'twig_extension.filter';
     }
   }

4. Create a twig function using class Twig_SimpleFunction. [file name:- TwigFunctionExtension.php]

   <?php
   namespace Drupal\twig_extension\TwigExtension;
   /**
    * Class TwigFunctionExtension.
    */
   class TwigFunctionExtension extends \Twig_Extension {
     /**
      * Declare your custom twig extension here
      *
      * @return array|\Twig_SimpleFunction[]
      */
     public function getFunctions() {
       return array(
         new \Twig_SimpleFunction('display_block_by_id',
           array($this, 'display_block'),
           array('is_safe' => array('html'))
         )
       );
     }
     /**
      * Function to get and render block by id
      * @param $block_id
      *  Block id to render
      *
      * @return array
      */
     public function display_block($block_id) {
       $block = \Drupal\block\Entity\Block::load($block_id);
       return \Drupal::entityTypeManager()
         ->getViewBuilder('block')
         ->view($block);
     }
     /**
      * {@inheritdoc}
      * @return string
      */
     public function getName() {
       return 'twig_extension.function';
     }
   }

We rarely need to develop a custom twig function and filter in Drupal 8 but we can successfully do this as described above.