fix(react-native): restore native proxy expandos

Author: DjDeveloperr

NativeScript/ffi/shared/jsi/NativeApiJsiHostObjects.h

@@ -977,20 +977,7 @@ class NativeApiObjectHostObject final
       return;
     }
 
-    if (property == "__nativeApiClassWrapper" ||
-        isNativeApiJsiExtendedClass(object_getClass(object_))) {
-      bridge_->setObjectExpando(runtime, object_, property, value);
-      return;
-    }
-
-    const char* className = object_getClassName(object_);
-    throw facebook::jsi::JSError(
-        runtime,
-        "Cannot assign JavaScript property '" + property +
-            "' to native proxy " +
-            (className != nullptr ? std::string(className) : std::string("")) +
-            ". Native proxies only accept writable native properties; keep "
-            "JavaScript state in a WeakMap or external object.");
+    bridge_->setObjectExpando(runtime, object_, property, value);
   }
 
   std::vector<PropNameID> getPropertyNames(Runtime& runtime) override {

packages/react-native/README.md

@@ -176,19 +176,20 @@ Context helpers cover common native view-manager patterns:
 
 ### State, delegates, and retention
 
-Do not attach arbitrary JavaScript properties to native proxies. Native proxies
-now reject unsupported/custom assignments with a guidance error. Keep JS state in
-`WeakMap`, React state, or another external object:
+Native proxies support JavaScript expando properties for local state. Native
+property setters still win first, and unsupported names fall back to JS state:
 
 ```ts
-const state = new WeakMap<UIView, {selected: boolean}>();
-
 NativeScript.runOnUI(() => {
   const view = UIView.new();
-  state.set(view, {selected: false});
+  view.ownerState = {selected: false};
+  view.tag = 42; // still calls UIKit's native tag setter
 });
 ```
 
+Use `WeakMap`, React state, or another external object when you want state that
+is not tied to the lifetime of a specific native proxy.
+
 UIKit often retains delegates and actions weakly or outlives the JavaScript
 closure that created them. Retain those helper objects explicitly. Use
 `ctx.retain()` inside `defineUIKitView()`, or a standalone retainer elsewhere:

test/react-native/ffi-compat/App.tsx

@@ -1273,16 +1273,36 @@ function buildReactNativeIntegrationTests(): TestCase[] {
       },
     },
     {
-      name: 'rejects arbitrary JavaScript state on native proxies with guidance',
+      name: 'preserves arbitrary JavaScript state on native proxies',
       async run() {
         await NativeScript.runOnUI(() => {
           const view = g('UIView').new();
-          assertThrows(
-            () => {
-              view.__nativeScriptCustomState = {unsafe: true};
-            },
-            /WeakMap|native proxy/,
-            'custom native proxy property assignment',
+          const state = {selected: true, count: 1};
+          view.__nativeScriptCustomState = state;
+          assert(
+            view.__nativeScriptCustomState === state,
+            'custom native proxy state identity',
+          );
+          view.__nativeScriptCustomState.count++;
+          assertEqual(
+            state.count,
+            2,
+            'custom native proxy state remains mutable',
+          );
+
+          view.__nativeScriptCustomFlag = 'ok';
+          assertEqual(
+            view.__nativeScriptCustomFlag,
+            'ok',
+            'custom native proxy string state',
+          );
+
+          view.tag = 42;
+          assertEqual(view.tag, 42, 'native property setter still wins');
+          assertEqual(
+            view.__nativeScriptCustomFlag,
+            'ok',
+            'custom native proxy state survives native property writes',
           );
         });
       },