Issue #3038365: Add the EntityOwnerInterface to BlockContent Entity

core/modules/block_content/js/form.es6.js

+/**
+ * @file
+ * Defines Javascript behaviors for the block content form.
+ */
+
+(function ($, Drupal) {
+  /**
+   * Behaviors for summaries for tabs in the block content edit form.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches summary behavior for tabs in the block content edit form.
+   */
+  Drupal.behaviors.blockContentFormSummaries = {
+    attach(context) {
+      const $context = $(context);
+
+      $context.find('.block-content-form-author').drupalSetSummary(context => {
+        const $authorContext = $(context);
+        const name = $authorContext.find('.field--name-uid input').val();
+
+        if (name) {
+          return Drupal.t('By @name', {'@name': name});
+        }
+      });
+    },
+  };
+})(jQuery, Drupal);