Check if it's the front page in the template

Question

Im trying to show content when I'm on the front page of my Drupal 8 test website, but the content shows on every page:

{% if front_page %}
  <header role="banner">
    {% if logo %}
      <a href="{{ front_page }}" title="{{ 'Home'|t }}" rel="home">
        <img src="{{ logo }}" alt="{{ 'Home'|t }}"/>
      </a>
    {% endif %}
    <h1 style="color:black">TESTTESTTESTESTAET</h1>
<h1>test</h1

    {{ page.header }}
  </header>
{% endif %}

Why doesn't this work and how can I make this work?

Answer 1

The variable you're looking for is called is_front:

{% if is_front %}

The available variables for a template are documented at the top of the .html.twig file, however there is also a set of default variables available to all templates (which are not documented in every single template). You can find them in _template_preprocess_default_variables().

Answer 2

Note that if you want to provide $variables['is_front'] to templates that doesn't, you can add this into the concerned preprocess function.

function themename_preprocess_menu(&$variables) {
  try {
    $variables['is_front'] = \Drupal::service('path.matcher')->isFrontPage();
  }
  catch (Exception $e) {
    $variables['is_front'] = FALSE;
  }
}

It is done the same way in template_preprocess_page for page.html.twig.

Same answer here

Answer 3

Assuming that the template you are using is page.html.twig, then the variable you are looking for is is_front; front_page contains the URL of the front page, initialized in template_preprocess_page() with the following code.

$variables['front_page'] = \Drupal::url('<front>');

For other template files, Drupal doesn't provide any variables telling you if the user is visiting the front page. Using code similar to the one used from template_preprocess_page(), you can set that variable in the preprocess function for the template you are using.

function mymodule_preprocess_HOOK(&$variables) {
  // An exception might be thrown.
  try {
    $variables['is_front'] = \Drupal::service('path.matcher')->isFrontPage();
  }
  catch (Exception $e) {
    // If the database is not yet available, set the default value.
    $variables['is_front'] = FALSE;
  }  
}

Replace HOOK with the template type (e.g. field for the field.hmtl.twig template).

Answer 4

You can get it directly in html.html.twig using root_path. It is already output on line 31 to set the body class:

{% if not root_path %}

CODE

{% endif %}

Answer 5

for field template this is the code that needs to be placed in mytheme.theme :

        function mytheme_preprocess_field(&$vars, $hook) {
          $element = &$vars['element'];
          if ($element['#field_name'] == 'field_page_paragraphs') {
            $vars['is_front'] = \Drupal::service('path.matcher')->isFrontPage();
          }
        }