diff --git a/core/modules/block/js/block.admin.js b/core/modules/block/js/block.admin.js
index 5c866c0..cc7b154 100644
--- a/core/modules/block/js/block.admin.js
+++ b/core/modules/block/js/block.admin.js
@@ -45,14 +45,14 @@ function showBlockEntry (index, block) {
 
         // Hide the category <details> if they don't have any visible rows.
         // Note that we first open all <details> to be able to use ':visible'.
-        $details.attr('open').each(hideCategoryDetails);
+        $details.attr('open', 'open').each(hideCategoryDetails);
       }
       else {
         $blocks.show();
         $details.show();
       }
       // Once the query is completely gone, close all details elements.
-      if (query.length == 0) {
+      if (query.length === 0) {
         $details.removeAttr('open');
       }
     }