Because of that letand classare not declared in the global scope ( read more ), you need to declare your class in an accessible area, such as:
window.a = class a{
static b(nr){
alert('and the answer is' + nr)
}
}
let aClassName = 'a',
aMethodeName = 'b',
theCompleteCall = 'a.b',
anArgument = 42;
, :
window[aClassName][aMethodeName](anArgument)
, , .