Call a imported js function in C++

[isml]

I have known that I can call a qml function in C++ using "QMetaObject::invokeMethod", but when the function is imported from an external js file in qml, I mean using:

// file main.qml
import "Handler.js" as Hander

// file Handler.js
function testCall() {

}

when I use "QMetaObject::invokeMethod(root, "Handler.testCall")", it does not work. How shoud I do?