Twig Blocks

What are Twig Blocks?

Twig blocks are used for inheritance and act as placeholders and replacements at the same time. Twig blocks can be thought of as holes to fill in in a Drupal page. Or perhaps as regions in your pages.

The challenge we face is having control of the markup while adhering to Drupal's best practices for rendering content. When the time to integrate a component with Drupal comes, oftentimes using include statements will do the job, but there are times when we want to modify content or markup before Drupal renders a component and include statements don't allow for this. We could use the extends Twig statements but these could also be limiting. In these situations the best option is to use Twig's embed statements. Embed statements combine the functionality of both, include and extends statements. Let's see an example.

card.twig

<article class="card{{- attributes ? ' ' ~ attributes.class -}}"
  {{- attributes ? attributes|without(class) -}}>
  {{ title_prefix }}
  {{ title_suffix }}
  ...
  {% block card_extra_content %}
  {% endblock %}
</article>

We've declared a twig block (card_extra_content), in which we can add or remove any content we want. The block on its own does nothing. Currently we added the Twig block as a placeholder to use later.

IMPORTANT: Twig blocks are not the same, or have anything to do with Drupal blocks.

paragraph--card.html.twig

{% embed '@training_theme/card/card.twig' with {
    heading: heading,
    image: content.field_image|render|trim is not empty ? content.field_image,
  }
%}
  {% block card_extra_content %}
    <h3>Hey this is new content</h3>
    <p>How cool is it that we can add or
    remove any content from here with twig blocks?</p>
  {% endblock %}
{% endembed %}