diff -u b/core/modules/block/js/block.admin.es6.js b/core/modules/block/js/block.admin.es6.js
--- b/core/modules/block/js/block.admin.es6.js
+++ b/core/modules/block/js/block.admin.es6.js
@@ -44,13 +44,13 @@
          *   The label of the block.
          */
         function toggleBlockEntry(index, label) {
-          var $label = $(label);
-          var $row = $label.parent().parent();
-          var labelMatch = $label.text().toLowerCase().indexOf(query) !== -1;
-          var categoryMatch = false;
+          const $label = $(label);
+          const $row = $label.parent().parent();
+          const labelMatch = $label.text().toLowerCase().indexOf(query) !== -1;
+          const categoryMatch = false;
 
           if (!labelMatch) {
-            var $category = $row.find('div.block-filter-category-source');
+            const $category = $row.find('div.block-filter-category-source');
             categoryMatch = $category.text().toLowerCase().indexOf(query) !== -1;
           }