Extending Twig functions and filters

Introduction

Twig is a powerful templating engine, used to output dynamic content safely and elegantly. While Drupal provides many Twig filters and functions out of the box, you might encounter situations where the built-in options are not enough. In such cases, you can create custom filters and functions that are reusable and tailored to your needs.

In this tutorial, you’ll learn how to define custom Twig extensions inside a custom module.

Step 1: Set Up a Custom Module

If you don’t already have a custom module, create one. For example:

Module name: custom_twig
Create the following file:

descriptioncustom_twig.info.yml

1name: 'Custom Twig'
2type: module
3description: 'Provides custom Twig filters and functions.'
4core_version_requirement: ^8 || ^9 || ^10
5package: Custom

Step 2: Create a Twig Extension Class

Inside your module, create a TwigExtension.php file in the src/Twig directory:

descriptioncustom_twig/src/Twig/TwigExtension.php

1<?php
2
3namespace Drupal\custom_twig\Twig;
4
5use Twig\Extension\AbstractExtension;
6use Twig\TwigFilter;
7use Twig\TwigFunction;
8
9class TwigExtension extends AbstractExtension {
10
11  public function getFilters() {
12    return [
13      new TwigFilter('reverse', [$this, 'reverseString']),
14    ];
15  }
16
17  public function getFunctions() {
18    return [
19      new TwigFunction('greet', [$this, 'greetUser']),
20    ];
21  }
22
23  public function reverseString($string) {
24    return strrev($string);
25  }
26
27  public function greetUser($name = 'Guest') {
28    return 'Hello, ' . $name . '!';
29  }
30}

Step 3: Register the Extension as a Service

Now tell Drupal to load your Twig extension by declaring it in a services.yml file.

descriptioncustom_twig.services.yml

1services:
2  custom_twig.twig_extension:
3    class: Drupal\custom_twig\Twig\TwigExtension
4    tags:
5      - { name: twig.extension }

Make sure this file is placed at the root of your module.

Step 4: Use Your Custom Filters and Functions in Twig

Once everything is set up and cache is cleared, you can use your custom logic directly in your Twig templates.

Example:

codeTWIG

1{{ 'Drupal'|reverse }}         {# Outputs: lapurD #}
2{{ greet('Alice') }}           {# Outputs: Hello, Alice! #}

Conclusion

Custom Twig extensions in Drupal allow you to move complex logic out of templates and into reusable PHP functions. This keeps your templates clean, readable, and maintainable. Once your module is enabled, these filters and functions can be used across all your themes and templates.

Drupal Masters