Overriding field values in Drupal 8

Question

I am attempting to override a node field value in Drupal 8 (on output) using template_preprocess_node. Specifically, I am attempting to override the text of a long text field. I am currently using this:

function THEMENAME_preprocess_node(&$variables) {
  $variables['content']['field_content'] = array(
    '#type' => 'markup',
    '#markup' => '<p>Testing 123</p>',
  );
}

And that works, but it totally overrides the field, removing the classes I added to the field wrapper, etc.

Does anyone know how to just set the value only, without replacing the entire field theming, etc? I do not want to manually add the field wrapper classes to #markup.

Answer 1

After doing a quick test, turns out that hook_preprocess_node will always override hook_preprocess_field's attributes.

Therefore, instead of adding the class in hook_preprocess_field, and if you don't want to use '#markup', you could add it in hook_preprocess_node like this:

function THEMENAME_preprocess_node(&$variables) {
    $variables['content']['field_test'] = array(
    '#type' => 'processed_text', 
    '#text' => 'Test 123',
    '#prefix' => '<div class="your-class">',
    '#suffix' => '</div>',
  );
}