Show the spinner right away

Resolves #18664

Author: brandonkelly

CHANGELOG.md

@@ -17,6 +17,7 @@
 - Fixed a bug where the “Max Authors” section setting was visible for Single sections.
 - Fixed an exception that would be thrown when attempting to access undefined keys within `craft\fields\data\JsonData` objects from Twig. ([#18656](https://github.com/craftcms/cms/issues/18656))
 - Fixed a bug where address cards could be missing their address preview. ([#18632](https://github.com/craftcms/cms/issues/18632))
+- Fixed a bug where the Save button’s spinner wouldn’t appear right away when saving a nested element in a slideout. ([#18664](https://github.com/craftcms/cms/discussions/18664))
 
 ## 5.9.18 - 2026-03-26
 

src/web/assets/cp/dist/cp.js

@@ -156,8 +156,10 @@ Craft.ElementEditorSlideout = Craft.CpScreenSlideout.extend(
       ev.stopPropagation();
       ev.stopImmediatePropagation();
 
+      this.showSubmitSpinner();
       await this.settings.onBeforeSubmit();
       this.elementEditor.handleSubmit(ev);
+      this.hideSubmitSpinner();
     },
 
     handleSubmitError: function (e) {