diff -u b/mathjax.module b/mathjax.module
--- b/mathjax.module
+++ b/mathjax.module
@@ -40,7 +40,6 @@
  * Implements hook_library_info_build().
  */
 function mathjax_library_info_build() {
-  global $base_url;
   $config = Drupal::config('mathjax.settings');
   $libraries = [];
   $libraries['source'] = [
@@ -56,7 +55,7 @@
   ];
   if ($config->get('use_cdn') == FALSE) {
     $libraries['source']['js'] = [
-      $base_url . '/libraries/MathJax/MathJax.js?config=TeX-AMS-MML_HTMLorMML' => [
+      \Drupal::request()->getBaseUrl() . '/libraries/MathJax/MathJax.js?config=TeX-AMS-MML_HTMLorMML' => [
         'type' => 'external',
         'minified' => TRUE,
       ],
only in patch2:
unchanged:
--- a/src/Form/MathjaxSettingsForm.php
+++ b/src/Form/MathjaxSettingsForm.php
@@ -130,7 +130,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
         ->set('config_type', $form_state->getValue('config_type'))
         ->set('config_string', $form_state->getValue('config_string'))
         ->save();
-
+    drupal_flush_all_caches();
     parent::submitForm($form, $form_state);
   }