GC behaviour wrt. native function vs. plain object vs. JS function

binding.cc

#include <stdio.h>
#include <node.h>

class WeakRef {
 public:
  WeakRef(v8::Isolate* isolate, v8::Local<v8::Value> func, const char* string):
      string_(string) {
    pers_.Reset(isolate, func);
    pers_.SetWeak(this, DeleteMe, v8::WeakCallbackType::kParameter);
  }
  ~WeakRef() {
    fprintf(stderr, "%s is dying\n", string_);
    pers_.ClearWeak();
    pers_.Reset();
  }
  static void DeleteMe(const v8::WeakCallbackInfo<WeakRef>& info) {
    delete info.GetParameter();
  }
 private:
  v8::Persistent<v8::Value> pers_;
  const char* string_;
};

static void TheFunction(const v8::FunctionCallbackInfo<v8::Value>& info) {
}

static void MakeFunction(const v8::FunctionCallbackInfo<v8::Value>& info) {
  v8::Isolate* isolate = info.GetIsolate();
  v8::Local<v8::Context> context = isolate->GetCurrentContext();
  v8::Local<v8::Function> the_function =
      v8::Function::New(context, TheFunction).ToLocalChecked();

  // Produce a message on stderr when this function is gc-ed.
  new WeakRef(isolate, the_function, "generated function");

  info.GetReturnValue().Set(the_function);
}

static void TrackJSFunction(const v8::FunctionCallbackInfo<v8::Value>& info) {
  // Produce a message on stderr when this function is gc-ed.
  new WeakRef(info.GetIsolate(), info[0], "JS function");
}

static void Init(v8::Local<v8::Object> exports,
                 v8::Local<v8::Value> module,
                 v8::Local<v8::Context> context) {
  v8::Isolate* isolate = context->GetIsolate();

  NODE_SET_METHOD(exports, "makeFunction", MakeFunction);
  NODE_SET_METHOD(exports, "trackJSFunction", TrackJSFunction);

  v8::Local<v8::Object> object = v8::Object::New(context->GetIsolate());

  // Produce on message on stderr when this object is gc-ed.
  new WeakRef(isolate, object, "object");

  exports->Set(context,
               v8::String::NewFromUtf8(isolate,
                                       "theObject",
                                       v8::NewStringType::kNormal)
                   .ToLocalChecked(),
               object).FromJust();
}

NODE_MODULE_CONTEXT_AWARE(NODE_GYP_MODULE_NAME, Init)

binding.gyp

  'targets': [
    {
      'target_name': 'binding',
      'sources': [ 'binding.cc' ]
    }
  ]
}

index.js

// Run with node --expose-gc index.js

const binding = require('./build/Release/binding');

let theFunction = binding.makeFunction();
let object = binding.theObject;
let functionToTrack = function functionToTrack() {};
binding.trackJSFunction(functionToTrack);

delete binding.theObject;

theFunction = null;
functionToTrack = null;
object = null;

gc();

package.json

{
  "name": "native-function-gc",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "Apache-2.0"
}