[ios] Fix weak objects implementation on Hermes

packages/expo-modules-core/ios/JSI/EXJavaScriptWeakObject.mm

@@ -13,9 +13,14 @@ @implementation EXJavaScriptWeakObject {
   __weak EXJavaScriptRuntime *_runtime;
 
   /**
-   Shared pointer to the `WeakRef` JS object.
+   Shared pointer to the `WeakRef` JS object. Available only on JSC engine.
    */
-  std::shared_ptr<jsi::Object> _jsObject;
+  std::shared_ptr<jsi::Object> _weakRef;
+
+  /**
+   A weak reference to a JS object. Available only on Hermes engine.
+   */
+  std::shared_ptr<jsi::WeakObject> _weakObject;
 }
 
 - (nonnull instancetype)initWith:(std::shared_ptr<jsi::Object>)jsObject
@@ -24,25 +29,39 @@ - (nonnull instancetype)initWith:(std::shared_ptr<jsi::Object>)jsObject
   if (self = [super init]) {
     _runtime = runtime;
 
+#if __has_include(<reacthermes/HermesExecutorFactory.h>)
+    _weakObject = std::make_shared<jsi::WeakObject>(*[runtime get], *jsObject);
+#else
     // Check whether the runtime supports `WeakRef` objects. If it does not,
     // we consciously hold a strong reference to the object and cause memory leaks.
-    // This is the case on hermes and JSC prior to iOS 14.5.
-    // TODO: (@tsapeta) Use `jsi::WeakObject` on hermes
+    // This is the case on JSC prior to iOS 14.5.
     if (expo::isWeakRefSupported(*[runtime get])) {
-      _jsObject = expo::createWeakRef(*[runtime get], jsObject);
+      _weakRef = expo::createWeakRef(*[runtime get], jsObject);
     } else {
-      _jsObject = jsObject;
+      _weakRef = jsObject;
     }
+#endif
   }
   return self;
 }
 
 - (nullable EXJavaScriptObject *)lock
 {
   jsi::Runtime *runtime = [_runtime get];
+
+#if __has_include(<reacthermes/HermesExecutorFactory.h>)
+  jsi::Value value = _weakObject->lock(*runtime);
+
+  // `lock` returns an undefined value if the underlying object no longer exists.
+  if (value.isUndefined()) {
+    return nil;
+  }
+  std::shared_ptr<jsi::Object> objectPtr = std::make_shared<jsi::Object>(value.asObject(*runtime));
+#else
   std::shared_ptr<jsi::Object> objectPtr = expo::isWeakRefSupported(*runtime)
-    ? expo::derefWeakRef(*runtime, _jsObject)
-    : _jsObject;
+    ? expo::derefWeakRef(*runtime, _weakRef)
+    : _weakRef;
+#endif
 
   if (!objectPtr) {
     return nil;