NodeJS Addon calling Javascript callback from inside NAN AsyncWorker::Execute - c++

Question

I would like to call a nodejs callback from within my asynchronous addon function. I have seen the synchronous example (here)
and I am using a wonderful asynchronous example (here) as a starting base.
However, when I try to execute a callback that was given to the c++ AsyncWorker child class, I get a Segmentation fault.
Here is my code:
#include <nan.h>
#include <functional>
#include <iostream>
#include <exception>
using namespace Nan;
using namespace v8;
using namespace std;
class ScriptWorker : public AsyncWorker {
public:
ScriptWorker(Callback *callback, const std::map<std::string, Callback*>)
: AsyncWorker(callback), script(script), cbs(cbs) {}
~ScriptWorker() {}
void Execute () {
// ------------------------
// Segmentation fault after
// ------------------------
Local<Value> argv[] = {
New<v8::Number>(id)
};
// -------------------------
// Segmentation fault before
// -------------------------
cbs["getUser"]->Call(1, argv);
}
private:
std::string script;
std::map<std::string, Callback*> cbs;
};
NAN_METHOD(Method) {
Local<Object> array = info[0]->ToObject();
Callback *callback = new Callback(info[1].As<Function>());
// Build up callbacks passed in from javascript.
// Will be a dynamic loop, but for now, hard code the one getUser example.
std::map<std::string, Callback*> cbs;
cbs.insert(std::pair<std::string, Callback*>("getUser",
new Callback(
array->Get(
v8::String::NewFromUtf8(v8::Isolate::GetCurrent(), "getUser")
).As<Function>()
)
));
AsyncQueueWorker(new ScriptWorker(callback, cbs));
}
NAN_MODULE_INIT(Init) {
Nan::Set(target, Nan::New<String>("hello").ToLocalChecked(), Nan::GetFunction(Nan::New<FunctionTemplate>(Method)).ToLocalChecked());
}
NODE_MODULE(hello, Init)
My questions:
Should I not use Nan's AsyncWorker and instead roll my own?
How do I setup the Execute function to call into Javascript?

Answer 1

EDIT:
See this repo:
https://github.com/xavero/node_addon_sample
it has a sample on how to work with callback functions and emitting events from C land.
You should not call v8/Nan functions in your Execute method of ScriptWorker, or you will get segment faults. Override the HandleOKCallback function to use the javascript callback.
To call from the javascript, in your c++ addon:
NAN_MODULE_INIT(Init) {
Nan::Set(target, Nan::New("myJsFunctionName").ToLocalChecked(),
Nan::GetFunction(Nan::New<FunctionTemplate>(Method)).ToLocalChecked());
}
NODE_MODULE(anyNameHere, Init)
And in your javascript:
// run "npm install bindings --save" in console first
var addon = require('bindings')('NativeExtension');
addon.myJsFunctionName({ foo: "bar"}, (arg1,arg2) => console.log(`${arg1} - ${arg2}`))