Matthieu Scarset
--- a/core/themes/starterkit_theme/js/reading-time.js 0 → 100644
+++ b/core/themes/starterkit_theme/js/reading-time.js 0 → 100644
+/**
+ * @file
+ * Defines a custom behavior.
+ */
+
+(function (Drupal, drupalSettings, once) {
--- a/core/themes/starterkit_theme/js/reading-time.js 0 → 100644
+++ b/core/themes/starterkit_theme/js/reading-time.js 0 → 100644
+   * @see starterkit_theme.libraries.yml
+   *   Where dependencies to core/drupalSettings and core/once are defined.
+   * @see https://www.drupal.org/docs/drupal-apis/javascript-api/javascript-api-overview
+   *   An introduction to the art of using JavaScript in Drupal.
+   * @see https://www.drupal.org/node/3158256
+   *   The change notice with examples of how to use once().
+   * @see https://www.npmjs.com/package/@drupal/once
+   *   The NPM package with the full documentation about once().
+   */
+  Drupal.behaviors.readingTime = {
+    attach(context) {
+      // Process the current content to calculate the reading time.
+      // We use `once()` from core to avoid processing the content multiple time.
+      once(onceName, elementSelector, context).forEach((element) => {
+        const time = readingTime(element, wordsPerMinute);
+        messages.add(