getter & setter for private objects

[memolus at googlemail.com]

I like to use getter and setter on private objects (e.g. "var test").
I didn't found any way to do this. I don't need sth. like
Object.definePrivateProperty, because I only want to set getter and
setter when I define the private object.

Example proposal:
var test;
get test = function() { [..] };
set test = function(newval) { [..] };

I'll be pleased to hear your feedback.