Creating a new Closure

[thestrangedev]

I want to create a decorator like this by Js

function Decorator (objectA) {

    return function (target, propertyKey, descriptor) {
        const backup = descriptor.value;

        descriptor.value = function (someParameters) {
            //do something with someParameters and objectA
            return backup.call(this, someParameters);
        }

        return descriptor;
    }
}

And my C++ code

Value Decorator (const CallbackInfo& info) {
    //do something...
    auto objectA = info[0].As<Object>();

    return Function::New(info.Env(), [objectA] (const CallbackInfo& info) -> Value {
       //do something...
        auto target = info[0].As<Object>();
	auto propertyKey = info[1].As<String>();
	auto descriptor = info[2].As<Object>();
        auto backup = descriptor.Get("value").As<Function>();

        descriptor.Set("value", Function::New(env, [backup, descriptor, objectA] (const CallbackInfo& info) -> Value {
            //I want to access backup, objectA, but they were already either deleted or changed to something new
        }

        return descriptor;
    }
}

With scalar types, I convert them to C++ types, so there's no problem. How about other types like object, function and array? I found the void* data argument can be passed to Funtion::New, but I didn't see any example.

[KevinEady]

Hi @thai6070 ,

The void* data argument of Function::New will allow you to set arbitrary data for the function call, such that this data can be retrieved via cbInfo.Data() inside the function's C++ implementation. Does this help? I'm not sure this actually solves your problem though, or what you are requesting an example / documentation of?

[Veetaha]

In simple words, I assume that the core problem here is that handles can't outlive the execution time of the invoked c++ handler.

[gabrielschulhof]

@thai6070 Hmmm ... we don't actually have a way of creating a weak reference with a callback.