Object transfer from javascript to c++

[wade-J]

Hi,
I know how to "expose C++ method to JavaScript in QML":http://qt-project.org/doc/qt-5/qtqml-cppintegration-exposecppattributes.html and data conversion will happen when parameters passing.So JavaScript objects will be convert to QVariantMap when used as C++ method parameters.

(1)But question is here, as I interpret, every time a new QVariantMap will be create as the parameter, how could we identify the object as in JavaScript where "===" could be used? Does Qt provide the way to do such thing？

(2)And what's more:
if we have a method "int foo(QVariantMap obj)" in C++, then we call it in JavaScript like this: CObj.foo(JSObj), how can we modify the attributes of JSObj in C++.
As far as I know, we should "create a component object in c++":http://qt-project.org/doc/qt-5/qtqml-cppintegration-interactqmlfromcpp.html ,and then call QMetaObject::invokeMethod to invoke JavaScript method in which we can change the JSObj attributes.Is there other way?

(3)What I also concern is the performance of creating a new QVariantMap of JSObj every time calling c++ method in JavaScript.

I need help, thanks for replying.