From 67fbd5ff1eef80d98e5e9c633a15bb1ae27134bb Mon Sep 17 00:00:00 2001
From: Kristiyan Kostadinov <crisbeto@abv.bg>
Date: Thu, 13 Nov 2025 11:32:10 +0100
Subject: [PATCH] fix(core): SSR error in signal forms

Resolves an SSR error, because we weren't checking if `MutationObserver` is available.

(cherry picked from commit 3f80ae74ba514903bcc083de5b67a02dc2cbc1ef)
---
 packages/core/src/render3/instructions/control.ts | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/render3/instructions/control.ts b/packages/core/src/render3/instructions/control.ts
index c8c591b366d..6c775c8074d 100644
--- a/packages/core/src/render3/instructions/control.ts
+++ b/packages/core/src/render3/instructions/control.ts
@@ -352,8 +352,16 @@ function listenToNativeControl(lView: LView<{} | null>, tNode: TNode, control: 
   // This means that we need to know when an `<option>` is created, destroyed, or has its `value`
   // changed so that we can re-sync the `<select>` to the field state's value. We implement this
   // using a `MutationObserver` that we create to observe `<option>` changes.
-  if (element instanceof HTMLSelectElement) {
-    const observer = observeSelectMutations(element, getControlDirective(tNode, lView)!);
+  if (
+    tNode.type === TNodeType.Element &&
+    tNode.value === 'select' &&
+    typeof MutationObserver === 'function'
+  ) {
+    const observer = observeSelectMutations(
+      element as HTMLSelectElement,
+      getControlDirective(tNode, lView)!,
+    );
+
     storeCleanupWithContext(tView, lView, observer, observer.disconnect);
   }
 }