diff -u b/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
--- b/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -814,13 +814,18 @@
   /**
    * An animated progress throbber and container element for AJAX operations.
    *
+   * @param {string|null} message
+   *   (optional) The message shown on the UI.
+   *
    * @return
    *   The HTML markup for the throbber.
    */
-  Drupal.theme.ajaxProgressThrobber = function(message) {
-    return '<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div>' +
-    Drupal.theme('ajaxProgressMessage', message) + '</div>';
-  }
+  Drupal.theme.ajaxProgressThrobber = function (message = null) {
+    const messageMarkup = message !== null ? Drupal.theme('ajaxProgressMessage', message) : '';
+    const throbber = '<div class="throbber">&nbsp;</div>';
+
+    return `<div class="ajax-progress ajax-progress-throbber">${throbber}${messageMarkup}</div>`;
+  };
 
   /**
    * An animated progress throbber and container element for AJAX operations.
@@ -828,20 +833,18 @@
    * @return
    *   The HTML markup for the throbber.
    */
-  Drupal.theme.ajaxProgressIndicatorFullscreen = function() {
+  Drupal.theme.ajaxProgressIndicatorFullscreen = function () {
     return '<div class="ajax-progress ajax-progress-fullscreen">&nbsp;</div>';
   };
 
   /**
-   * Formats optional text accompanying the AJAX progress throbber.
+   * Formats text accompanying the AJAX progress throbber.
    *
    * @return
    *   The HTML markup for the throbber.
    */
-  Drupal.theme.ajaxProgressMessage = function(message) {
-    if (message) {
-      return '<div class="message">' + message + '</div>';
-    }
+  Drupal.theme.ajaxProgressMessage = function (message) {
+    return `<div class="message">${message}</div>`;
   };
 
   /**
diff -u b/core/misc/ajax.js b/core/misc/ajax.js
--- b/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -368,8 +368,13 @@
     }
   };
 
-  Drupal.theme.ajaxProgressThrobber = function (message) {
-    return '<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div>' + Drupal.theme('ajaxProgressMessage', message) + '</div>';
+  Drupal.theme.ajaxProgressThrobber = function () {
+    var message = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : null;
+
+    var messageMarkup = message !== null ? Drupal.theme('ajaxProgressMessage', message) : '';
+    var throbber = '<div class="throbber">&nbsp;</div>';
+
+    return '<div class="ajax-progress ajax-progress-throbber">' + throbber + messageMarkup + '</div>';
   };
 
   Drupal.theme.ajaxProgressIndicatorFullscreen = function () {
@@ -377,9 +382,7 @@
   };
 
   Drupal.theme.ajaxProgressMessage = function (message) {
-    if (message) {
-      return '<div class="message">' + message + '</div>';
-    }
+    return '<div class="message">' + message + '</div>';
   };
 
   Drupal.Ajax.prototype.setProgressIndicatorBar = function () {
only in patch2:
unchanged:
--- a/core/modules/field_ui/field_ui.es6.js
+++ b/core/modules/field_ui/field_ui.es6.js
@@ -219,7 +219,7 @@
 
       if (rowNames.length) {
         // Add a throbber next each of the ajaxElements.
-        $(ajaxElements).after('<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div></div>');
+        $(ajaxElements).after(Drupal.theme.ajaxProgressThrobber());
 
         // Fire the Ajax update.
         $('input[name=refresh_rows]').val(rowNames.join(' '));
only in patch2:
unchanged:
--- a/core/modules/field_ui/field_ui.js
+++ b/core/modules/field_ui/field_ui.js
@@ -126,7 +126,7 @@
       });
 
       if (rowNames.length) {
-        $(ajaxElements).after('<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div></div>');
+        $(ajaxElements).after(Drupal.theme.ajaxProgressThrobber());
 
         $('input[name=refresh_rows]').val(rowNames.join(' '));
         $('input[data-drupal-selector="edit-refresh"]').trigger('mousedown');