I’m creating a custom module to execute some JS AFTER the cache is cleared. Here is the structure of the module:

Module -> flush.info.yml

name: Flush type: module description: A very important module. package: Custom version: 1.0 core_version_requirement: ^8 || ^9 

Module -> flush.libraries.yml

flush:   version: 1.x   js:     js/flush.js: {}   dependencies:     - core/jquery     - core/drupalSettings 

Module -> flush.module

<?php  use DrupalCoreFormFormStateInterface;  /**  * Implementation of hook_cache_flush()  */    function flush_cache_flush() {     Drupal::state()->set('flush_cache_cleared', TRUE);   }    function flush_page_attachments(array &$attachments) {     if (Drupal::state()->get('flush_cache_cleared')) {       $attachments['#attached']['library'][] = 'flush/flush';      Drupal::state()->set('flush_cache_cleared', FALSE);     }   } 

Module -> JS -> flush.js

(function ($, Drupal, drupalSettings) {     'use strict';      Drupal.behaviors.flush = {       /**        * Drupal attach behavior.        */       attach: function (context, settings) {         this.settings = this.getSettings(settings);         alert("flush!");         console.log ("Hello World");       },     };   })(jQuery, Drupal, drupalSettings); 

Both functions in flush.module work properly, however the JS that is #attached which is simply supposed to use an alert() never runs. I believe the issue is related to this line specifically : $attachments['#attached']['library'][] = 'flush/flush';

Is there something obvious I’m doing wrong? I used page_attachments as the method to attach the JS because it does not necessarily have to be associated with a specific part of the page, or a render array, etc. Please let me know if you have any potential ideas as to what the issue could be, thanks!