How to create a getter in node add-on?

Question

I have been in the process of writing a node add-on, and I cannot seem to figure out how add a property to a class. What I have been doing is creating a method in the c++ add-on, and in the javascript I create a getter that calls the function in the add-on.

Is this the correct way to do this, or can this property be created in the c++ add-on?

In the c++ I do this:

void MyAddon::Init(Local<Object> exports, Local<Object> module) {

  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
  tpl->SetClassName(String::NewFromUtf8(isolate, "MyAddon"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);

  // Add the property
  NODE_SET_PROTOTYPE_METHOD(tpl, "currWidth", Width);


  // Export the class
  constructor.Reset(isolate, tpl->GetFunction());
  exports->Set(
      String::NewFromUtf8(isolate, "MyAddon"), tpl->GetFunction());
}

Then in the JavaScript I do this:

const MyAddon = require('./build/Release/MyAddon')

module.exports.Addon = class Addon extends MyAddon.MyAddon {
  get width() { return this.currWidth() }
}

This doesn't seem like the correct way to add a property to the add-on. The example on the website uses NODE_SET_METHOD, so I tried but it doesn't run the method. I don't get any errors either. The method just doesn't run...

In there example they don't try to set it on a class, which is what I am trying to do, so mine is a little different:

NODE_SET_METHOD((Local<Template>)tpl, "height", Height);

How can I create this property in the c++?

Answer 1

In the Init method, it was as easy as adding this line:

tpl->InstanceTemplate()->SetAccessor(String::NewFromUtf8(isolate, "width"), Width);

And creating a method that looks like this:

void MyAddon::Width(Local<String> property, const PropertyCallbackInfo<Value> &args) {}