Issue #1684822 by droplet: JSHint block.

core/modules/block/block.js

-(function ($) {
+(function ($, window) {
 
 "use strict";
 
@@ -90,7 +90,7 @@ Drupal.behaviors.blockDrag = {
       // Check whether the newly picked region is available for this block.
       if (regionField.find('option[value=' + regionName + ']').length === 0) {
         // If not, alert the user and keep the block in its old region setting.
-        alert(Drupal.t('The block cannot be placed in this region.'));
+        window.alert(Drupal.t('The block cannot be placed in this region.'));
         // Simulate that there was a selected element change, so the row is put
         // back to from where the user tried to drag it.
         regionField.change();
@@ -148,4 +148,4 @@ Drupal.behaviors.blockDrag = {
   }
 };
 
-})(jQuery);
+})(jQuery, window);