QML : how to pass javascript function as argument in another function

I have QML code, for example this code http://stackoverflow.com/questions/27945427/qml-how-to-pass-javascript-function-as-argument-in-another-function [stackoverflow.com] in normal javascript this works cool, but when I use this code in QML the bad thing is visitFun always has type of undefined, and it does not work.. any idea how to make this work ?