How to use complex v8 datatypes in an async worker class of a native node module?

Question

I try to make my node module methods asynchronous. I created an AsyncWorker Class but stumbling on a few things :/

My Nan::AsyncWorker looks as follows...

class PackerWorker : public Nan::AsyncWorker {
 public:
  PackerWorker(Nan::Callback *callback, v8::Handle<v8::Array> messageFields)
    : AsyncWorker(callback), messageFields(messageFields) {}
  ~PackerWorker() {}

  // Executed inside the worker-thread.
  // It is not safe to access V8, or V8 data structures
  // here, so everything we need for input and output
  // should go on `this`.
  void Execute () {
    //pack_iso8583(messageFields);
  }

  // Executed when the async work is complete
  // this function will be run inside the main event loop
  // so it is safe to use V8 again
  void HandleOKCallback () {
    //Nan::HandleScope scope;
    v8::Local<v8::Value> argv[] = { // currently just dummy values need to return v8::Local<v8::Array> result here!
        Nan::Null()
      , Nan::New<v8::Number>(1.75) 
    };

    callback->Call(2, argv);
  }

 private:
  v8::Handle<v8::Array> messageFields;
  //v8::Local<v8::Array> result;
};

--

  void Execute () {
    result = pack_iso8583(messageFields);
  }

When I implement this method the call crash without additional informations. Further reading point out that it is not safe to access V8, or V8 data structures. So I think this is the reason because the sync method works.

1. Do I need to convert all variables to Nan datatypes? If so what is the equivalent in Nan:: to v8::Local<v8::Array> and v8::Handle<v8::Array> and how convert them and vice versa?
2. How to get usefull exception information when the C++ code fails to execute?

The complete source code is available here: https://github.com/s-a/iso-8583/blob/30ac35796ba5014ad5668ac2919fddcb3b082580/functions.cc#L144. Just clone the repo and npm install and npm test

Maybe someone like to create a PR :), anyway I am very pleased about any helping hints! I just hoped it would be more trivial to make existing methods asynchronous ^^