twig-templating

Twig Templating

Always use {{ attach_library() }} for assets — never inline CSS/JS. Always use BEM naming for custom classes. Avoid heavy logic in templates — prefer preprocess functions. Never use |raw on user input.

Template Naming Conventions

Drupal uses suggestion-based template discovery:

node.html.twig                    # Base node template.
node--article.html.twig           # Article content type.
node--article--teaser.html.twig   # Article teaser view mode.
node--42.html.twig                # Specific node by ID.

block.html.twig                   # Base block template.
block--system-branding-block.html.twig  # Specific block.

field.html.twig # Base field template. field--field-image.html.twig # Specific field. field--node--field-image--article.html.twig # Field + bundle.

page.html.twig # Base page template. page--front.html.twig # Front page. page--node--42.html.twig # Specific node page.

## Template Structure

```twig
{# node--article.html.twig #}
{% set classes = [
  'node',
  'node--' ~ node.bundle,
  node.isPromoted() ? 'node--promoted',
  node.isSticky() ? 'node--sticky',
  view_mode ? 'node--' ~ view_mode,
] %}

<article{{ attributes.addClass(classes) }}>
  {% if label %}
    <h2{{ title_attributes }}>
      <a href="{{ url }}" rel="bookmark">{{ label }}</a>
    </h2>
  {% endif %}

  <div{{ content_attributes.addClass('node__content') }}>
    {{ content }}
  </div>
</article>

Common Filters

Filter	Purpose	Example
`	t`	Translate string
`	raw`	Skip auto-escape (CAUTION)
`	escape`	Explicit escape
`	clean_class`	CSS-safe class
`	clean_id`	HTML-safe ID
`	date`	Format date
`	length`	Array/string length
`	without`	Render without fields
`	safe_join`	Join array with separator

Drupal-Specific Functions

{# Attach library assets. #}
{{ attach_library('my_theme/component') }}

{# Link to a route. #}
{{ path('entity.node.canonical', {'node': nid}) }}

{# Create a link. #}
{{ link('Click here', url) }}

{# Translate with context. #}
{{ 'Submit'|t({}, {'context': 'my_module'}) }}

{# Access Drupal URL. #}
{{ url('<front>') }}

{# File URL from URI. #}
{{ file_url(node.field_image.entity.fileuri) }}

Preprocess Functions

/**
 * Implements hook_preprocess_HOOK() for node templates.
 */
function my_theme_preprocess_node(array &$variables): void {
  $node = $variables['node'];

  // Add custom variables.
  $variables['reading_time'] = ceil(str_word_count(strip_tags($node->body->value)) / 200);

  // Add conditional classes.
  if ($node->isPublished()) {
    $variables['attributes']['class'][] = 'node--published';
  }
}

Template Suggestions

/**
 * Implements hook_theme_suggestions_HOOK_alter() for node templates.
 */
function my_theme_theme_suggestions_node_alter(array &$suggestions, array $variables): void {
  $node = $variables['elements']['#node'];

  // Add suggestion based on custom field value.
  if ($node->hasField('field_layout') && !$node->get('field_layout')->isEmpty()) {
    $layout = $node->get('field_layout')->value;
    $suggestions[] = 'node__' . $node->bundle() . '__' . $layout;
  }
}

BEM Component Pattern

{# components/card.html.twig #}
{% set card_classes = [
  'card',
  variant ? 'card--' ~ variant,
  size ? 'card--' ~ size,
] %}

<div{{ attributes.addClass(card_classes) }}>
  {% if image %}
    <div class="card__image">
      {{ image }}
    </div>
  {% endif %}

  <div class="card__content">
    {% if title %}
      <h3 class="card__title">{{ title }}</h3>
    {% endif %}

    {% if body %}
      <div class="card__body">{{ body }}</div>
    {% endif %}
  </div>

  {% if actions %}
    <div class="card__actions">{{ actions }}</div>
  {% endif %}
</div>

Template Best Practices

1. Keep logic minimal in Twig - heavy logic goes to preprocess functions.
2. Use BEM naming convention (block__element--modifier).
3. Always use {{ attach_library() }} for component assets.
4. Use |t filter for all translatable strings.
5. Templates receive data only - no data fetching in Twig.
6. Disable Twig debug in production configuration.
7. Use {{ content|without('field_name') }} to exclude specific fields.