Issue #3437801 by Mingsong: Drupal in a subdirectory

js/entity_reference_tree.js

@@ -63,11 +63,7 @@
             treeContainer.jstree({
               core: {
                 data: {
-                  url: function(node) {
-                    return Drupal.url(
-                      dataURL
-                    );
-                  },
+                  url: dataURL,
                   data: function(node) {
                     return {
                       id: node.id,

src/Form/SearchForm.php

@@ -164,10 +164,10 @@ class SearchForm extends FormBase {
 
     // Pass data to js file.
     $form['#attached']['drupalSettings'] = [
-      'data_url_' . $field_edit_id => mb_substr(Url::fromRoute('entity_reference_tree.json', [
+      'data_url_' . $field_edit_id => Url::fromRoute('entity_reference_tree.json', [
         'entity_type' => $entity_type,
         'bundles' => $bundles,
-      ])->toString(), 1) . '?token=' . \Drupal::csrfToken()->get($bundles),
+      ])->toString() . '?token=' . \Drupal::csrfToken()->get($bundles),
       'tree_limit_' . $field_edit_id => empty($limit) ? -1 : $limit,
     ];