From d34a9c577816e8136425b3db13dcdda2c63413d2 Mon Sep 17 00:00:00 2001
From: ownedbywuigi <ownedbywuigi@gmail.com>
Date: Fri, 27 Mar 2026 11:34:40 +0000
Subject: [PATCH] Refactor MaybeCheckSameAttrVal to streamline old value
 storage for custom elements

---
 dom/base/Element.cpp | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index 364022644d..18858a159f 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -2336,6 +2336,7 @@ Element::MaybeCheckSameAttrVal(int32_t aNamespaceID,
                                bool* aOldValueSet)
 {
   bool modification = false;
+  CustomElementData* customElementData = GetCustomElementData();
   *aHasListeners = aNotify &&
     nsContentUtils::HasMutationListeners(this,
                                          NS_EVENT_BITS_MUTATION_ATTRMODIFIED,
@@ -2351,13 +2352,14 @@ Element::MaybeCheckSameAttrVal(int32_t aNamespaceID,
   if (*aHasListeners || aNotify) {
     BorrowedAttrInfo info(GetAttrInfo(aNamespaceID, aName));
     if (info.mValue) {
-      // Check whether the old value is the same as the new one.  Note that we
-      // only need to actually _get_ the old value if we have listeners or
-      // if the element is a custom element (because it may have an
-      // attribute changed callback).
-      if (*aHasListeners || GetCustomElementData()) {
-        // Need to store the old value.
-        //
+      bool valueMatches = aValue.EqualsAsStrings(*info.mValue);
+      if (valueMatches && aPrefix == info.mName->GetPrefix()) {
+        return true;
+      }
+
+      // Need to store the old value if listeners are present or this is a
+      // custom element that may run an attribute-changed callback.
+      if (*aHasListeners || customElementData) {
         // If the current attribute value contains a pointer to some other data
         // structure that gets updated in the process of setting the attribute
         // we'll no longer have the old value of the attribute. Therefore, we
@@ -2368,10 +2370,7 @@ Element::MaybeCheckSameAttrVal(int32_t aNamespaceID,
         aOldValue.SetToSerialized(*info.mValue);
         *aOldValueSet = true;
       }
-      bool valueMatches = aValue.EqualsAsStrings(*info.mValue);
-      if (valueMatches && aPrefix == info.mName->GetPrefix()) {
-        return true;
-      }
+
       modification = true;
     }
   }