Access array in object via NAN

array_prop.cpp

// JS calling code
var obj = {
    a: 5,
    b : [1, 2, 3]
}

addon.add_array(obj);
assert(obj.b[0] == 6);
assert(obj.b[1] == 7);
assert(obj.b[2] == 8);
/////////////////////////

// accept object with a number "a" and an array "b".  Add a to all b values.
NAN_METHOD(AddArray) {
    if ( info.Length() > 0 ) {
        // initial input parameter is an object
        Local<Object> input = info[0]->ToObject();
        Local<String> a_prop = Nan::New<String>("a").ToLocalChecked();
        Local<String> b_prop = Nan::New<String>("b").ToLocalChecked();
        
        // Use NumberValue to get the number property named a
        double a = Nan::Get(input, a_prop).ToLocalChecked()->NumberValue();
        // Use Cast to get the array property named b
        Local<Array> b = Local<Array>::Cast(Nan::Get(input, b_prop).ToLocalChecked());
        
        for (unsigned int i = 0; i < b->Length(); i++ ) {
            if (Nan::Has(b, i).FromJust()) {
                // get data from a particular index
                double value = Nan::Get(b, i).ToLocalChecked()->NumberValue();
                
                // set a particular index - note the array parameter
                // is mutable
                Nan::Set(b, i, Nan::New<Number>(value + a));
            }
        }
    }
}

NAN_MODULE_INIT(Init) {
    Nan::Set(target, New<String>("add_array").ToLocalChecked(),
        GetFunction(New<FunctionTemplate>(AddArray)).ToLocalChecked());
}

NODE_MODULE(my_addon, Init)