ES6 class variable alternatives

Question

Currently in ES5 many of us are using the following pattern in frameworks to create classes and class variables, which is comfy:

Answer 1

This is a bit hackish combo of static and get works for me

class ConstantThingy{
        static get NO_REENTER__INIT() {
            if(ConstantThingy._NO_REENTER__INIT== null){
                ConstantThingy._NO_REENTER__INIT = new ConstantThingy(false,true);
            }
            return ConstantThingy._NO_REENTER__INIT;
        }
}

elsewhere used

var conf = ConstantThingy.NO_REENTER__INIT;
if(conf.init)...