Add napi_finalize override to ObjectWrap

doc/object_wrap.md

@@ -190,6 +190,17 @@ property of the `Napi::CallbackInfo`.
 
 Returns a `Napi::Function` representing the constructor function for the class.
 
+### Finalize
+
+Provides an opportunity to run cleanup code that requires access to the `Napi::Env` 
+before the wrapped native object instance is freed.  Override to implement. 
+
+```cpp
+virtual void Finalize(Napi::Env env);
+```
+
+- `[in] env`: `Napi::Env`.
+
 ### StaticMethod
 
 Creates property descriptor that represents a static method of a JavaScript class.

napi-inl.h

@@ -3259,6 +3259,9 @@ inline ClassPropertyDescriptor<T> ObjectWrap<T>::InstanceValue(
   return desc;
 }
 
+template <typename T>
+inline void ObjectWrap<T>::Finalize(Napi::Env env) {}
+
 template <typename T>
 inline napi_value ObjectWrap<T>::ConstructorCallbackWrapper(
     napi_env env,
@@ -3400,8 +3403,9 @@ inline napi_value ObjectWrap<T>::InstanceSetterCallbackWrapper(
 }
 
 template <typename T>
-inline void ObjectWrap<T>::FinalizeCallback(napi_env /*env*/, void* data, void* /*hint*/) {
+inline void ObjectWrap<T>::FinalizeCallback(napi_env env, void* data, void* /*hint*/) {
   T* instance = reinterpret_cast<T*>(data);
+  instance->Finalize(Napi::Env(env));
   delete instance;
 }
 

napi.h

@@ -1657,6 +1657,7 @@ namespace Napi {
     static PropertyDescriptor InstanceValue(Symbol name,
                                             Napi::Value value,
                                             napi_property_attributes attributes = napi_default);
+    virtual void Finalize(Napi::Env env);
 
   private:
     static napi_value ConstructorCallbackWrapper(napi_env env, napi_callback_info info);

test/objectwrap.cc

@@ -24,6 +24,11 @@ class Test : public Napi::ObjectWrap<Test> {
 public:
   Test(const Napi::CallbackInfo& info) :
     Napi::ObjectWrap<Test>(info) {
+
+    if(info.Length() > 0) {
+      finalizeCb_ = Napi::Persistent(info[0].As<Napi::Function>());
+    }
+
   }
 
   void Setter(const Napi::CallbackInfo& /*info*/, const Napi::Value& value) {
@@ -105,8 +110,20 @@ class Test : public Napi::ObjectWrap<Test> {
     }));
   }
 
+  void Finalize(Napi::Env env) {
+
+    if(finalizeCb_.IsEmpty()) {
+      return;
+    }
+
+    finalizeCb_.Call(env.Global(), {Napi::Boolean::New(env, true)});
+    finalizeCb_.Unref();
+
+  }
+
 private:
   std::string value_;
+  Napi::FunctionReference finalizeCb_;
 };
 
 Napi::Object InitObjectWrap(Napi::Env env) {

test/objectwrap.js

@@ -182,6 +182,24 @@ const test = (binding) => {
     }
   };
 
+  const testFinalize = (clazz) => {
+
+    let finalizeCalled = false;
+    const finalizeCb = function(called) {
+      finalizeCalled = called;
+    };
+
+    //Scope Test instance so that it can be gc'd.
+    (function() {
+      new Test(finalizeCb);
+    })();
+
+    global.gc();
+
+    assert.strictEqual(finalizeCalled, true);
+
+  };
+
   const testObj = (obj, clazz) => {
     testValue(obj, clazz);
     testAccessor(obj, clazz);
@@ -197,7 +215,8 @@ const test = (binding) => {
     testStaticAccessor(clazz);
     testStaticMethod(clazz);
 
-    testStaticEnumerables(clazz);
+    testStaticEnumerables(clazz);    
+    testFinalize(clazz);
   };
 
   // `Test` is needed for accessing exposed symbols