I am trying to load an asset library in my Drupal 8 custom theme. I have created the library and can load it via mytheme.info.yml file. However, if I try the load it using hook_page_attachments() in the mytheme.theme file, then the function is not called.

I did a search for this function in the Drupal 8 standard installation and it only ever seems to be called from modules. Can hook_page_attachments only be called from modules? Any suggestions on why this is not working.

mytheme.theme file content:

function mytheme_page_attachments(array &$attachments) {
  $attachments ['#attached']['library'][] = 'mytheme/general-js';

1 Answer 1


It appears that this function is only callable from a module, as it is listed in Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 module but not listed as a valid method in Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 theme.

It should be noted that the related function hook_page_attachments_alter() can be called from the theme layer (i.e. can be called from mytheme.theme file).

function mytheme_page_attachments_alter(&$page) {
  $page['#attached']['library'][] = 'mytheme/general-js';

Alternatively one can attach libraries to a page from within hook_preprocess_page()

function mytheme_preprocess_page(&$variables) {
  $variables['#attached']['library'][] = 'mytheme/cuddly-slider';

The advantage of these two methods is that it enables one to utilize logic/code to determine whether or not to attach a library to a page.

  • Another bennefit of using these methods is attaching inline scripts to the head of a page. For example, the "advanced" typekit script, or a google analytics script you want to manually code in. Good instructions on how to here: drupal.org/node/2642476#comment-11838322 May 17, 2017 at 14:01
  • A bit misleading, that hook_page_attachments is placed in theme.api.php: api.drupal.org/api/drupal/…
    – NicklasF
    Feb 17, 2023 at 21:23

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