ecmascript 6 how to call a static class methode by reflection

So I would like to call an es 6 static class method By reflection using a string className and a string method name. I have tried several ways. unfortunately I don’t seem to find the correct way to do this.

Can anybody help?

class a{
        static b(nr){
        alert('and the answer is' + nr)
  }
}

let aClassName = 'a',
                aMethodeName = 'b',
    theCompleteCall = 'a.b',
    anArgument = 42;

//Reflect.apply(theCompleteCall,anArgument);
//window[aClassName][aMethodeName](anArgument);
//window[theCompleteCall](anArgument);