Issue #3397785 by yash.rode, srishtiiee, lauriii, smustgrave: Dialog focus is...

Issue #3397785 by yash.rode, srishtiiee, lauriii, smustgrave: Dialog focus is returned to dialog instead of first tabbable element on dialog AJAX update

(cherry picked from commit 762fcae9)

core/misc/dialog/dialog.ajax.js

@@ -38,11 +38,16 @@
           $dialog.trigger('dialogButtonsChange');
         }
 
-        // If the body element has focus, it means focus was effectively lost.
-        // In these instances, force focus on the dialog.
-        if (document.activeElement === document.body) {
-          $dialog.dialog('widget').trigger('focus');
-        }
+        setTimeout(function () {
+          // Account for pre-existing focus handling that may have already moved
+          // the focus inside the dialog.
+          if (!$dialog[0].contains(document.activeElement)) {
+            // Move focus to the first focusable element in the next event loop
+            // to allow dialog buttons to be changed first.
+            $dialog.dialog('instance')._focusedElement = null;
+            $dialog.dialog('instance')._focusTabbable();
+          }
+        }, 0);
       }
 
       const originalClose = settings.dialog.close;

core/tests/Drupal/FunctionalJavascriptTests/Ajax/DialogTest.php

@@ -167,8 +167,12 @@ public function testDialog() {
     // Press buttons in the dialog to ensure there are no AJAX errors.
     $this->assertSession()->elementExists('css', '.ui-dialog-buttonpane')->pressButton('Hello world');
     $this->assertSession()->assertWaitOnAjaxRequest();
+    $has_focus_text = $this->getSession()->evaluateScript('document.activeElement.textContent');
+    $this->assertEquals('Do it', $has_focus_text);
     $this->assertSession()->elementExists('css', '.ui-dialog-buttonpane')->pressButton('Preview');
     $this->assertSession()->assertWaitOnAjaxRequest();
+    $has_focus_text = $this->getSession()->evaluateScript('document.activeElement.textContent');
+    $this->assertEquals('Do it', $has_focus_text);
 
     // Reset: close the form.
     $form_dialog->findButton('Close')->press();