From dded150fa8a61bbad0f5f54900e4c7d0b87b17fd Mon Sep 17 00:00:00 2001
From: Michael Price <mikepricedev@gmail.com>
Date: Mon, 22 Jul 2019 22:10:14 -0600
Subject: [PATCH] Allows for overriding Napi::ObjectWrap::FinalizeCallback.

---
 doc/object_wrap.md | 39 +++++++++++++++++++++++++++++++++++++++
 napi-inl.h         |  2 +-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/doc/object_wrap.md b/doc/object_wrap.md
index 31be140f0..ab597adf6 100644
--- a/doc/object_wrap.md
+++ b/doc/object_wrap.md
@@ -544,3 +544,42 @@ name of the property.
 One or more of `napi_property_attributes`.
 
 Returns `Napi::PropertyDescriptor` object that represents an instance value
+
+### FinalizeCallback
+
+Allows user to be notified when externally-owned data is ready to be cleaned up 
+because the object with which it was associated with, has been garbage-collected.
+
+```cpp
+static void T::FinalizeCallback(napi_env env, void* data, void* hint);
+```
+
+- `[in] env`: `napi_env`.
+- `[in] data`: pointer to the native instance.  Must be cast in method e.g.
+    `reinterpret_cast<T*>(data)`.
+- `[in] hint`: Optional contextual hint that is passed to the finalize callback.
+
+`T::FinalizeCallback`is optional, defined on the derived class, must be public 
+and implements [napi_finalize](https://nodejs.org/api/n-api.html#n_api_napi_finalize "N-API napi_finalize documentation").
+
+NOTE: Overrides default `Napi::ObjectWrap::FinalizeCallback`. The default 
+`Napi::ObjectWrap::FinalizeCallback` frees the native instance.  A user defined 
+finalzier is, therefore, responsible for freeing the native instance.
+
+```cpp
+#include <napi.h>
+class Example : public Napi::ObjectWrap<Example> {
+  public:
+  static void FinalizeCallback(napi_env env, void* data, void* hint);
+  //...
+};
+
+void Example::FinalizeCallback(napi_env env, void* data, void* hint)
+{
+  Example* instance = reinterpret_cast<Example*>(data);
+  //Do stuff...
+
+  //Free native instance
+  delete instance;
+}
+```
\ No newline at end of file
diff --git a/napi-inl.h b/napi-inl.h
index 0db3c9830..3c7a32a44 100644
--- a/napi-inl.h
+++ b/napi-inl.h
@@ -2879,7 +2879,7 @@ inline ObjectWrap<T>::ObjectWrap(const Napi::CallbackInfo& callbackInfo) {
   napi_status status;
   napi_ref ref;
   T* instance = static_cast<T*>(this);
-  status = napi_wrap(env, wrapper, instance, FinalizeCallback, nullptr, &ref);
+  status = napi_wrap(env, wrapper, instance, T::FinalizeCallback, nullptr, &ref);
   NAPI_THROW_IF_FAILED_VOID(env, status);
 
   Reference<Object>* instanceRef = instance;