Passing an object to a Node.js C++ Addon

Question

https://medium.com/@muehler.v/tutorial-to-node-js-native-c-modules-part-2-arrays-json-and-callbacks-9b81f09874cd

I am following along with the above article trying to access a string in an object that is passed to a C++ node addon function. My function is below but I am unable to get it the addon to compile. When I do I get the error:

../addon.cpp:239:26: error: no viable conversion from 'MaybeLocal<v8::Value>' (aka 'v8::MaybeLocal<v8::Value>') to 'v8::Local<v8::Value>'
    v8::Local<v8::Value> pwdValue = Nan::Get(obj, pwdProp);
                         ^          ~~~~~~~~~~~~~~~~~~~~~~

Any ideas on how I might resolve this error? Thanks

NAN_METHOD(init) {
  v8::Local<v8::Object> obj = info[0]->ToObject();
  v8::Local<v8::String> pwdProp = Nan::New("PWD").ToLocalChecked();

  std::string pwd = "";

  if (Nan::HasOwnProperty(obj, pwdProp).FromJust()) {
    v8::Local<v8::Value> pwdValue = Nan::Get(obj, pwdProp);
    pwd = std::string(*Nan::Utf8String(pwdValue->ToString()));
  }

  std::cout << pwd << std::endl;
}

justadudewhohacks · Accepted Answer · 2018-05-11 06:30:13Z

1

Nan::Get returns a MaybeLocal, which might be empty for reasons mentioned in the docs.

You can get the Local handle from a MaybeLocal by using .ToLocalChecked() as follows: v8::Local<v8::Value> pwdValue = Nan::Get(obj, pwdProp).ToLocalChecked();.

To check whether the MaybeLocal actually holds a value, you can check bool isEmpty = Nan::Get(obj, pwdProp).IsEmpty().

answered May 11, 2018 at 6:30

justadudewhohacks

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