JSFiddle - React, Tailwind, and code Playground

JavaScript

let A1 = (function() {
  class A {
    fn() {}
  }
  return A;
})();

let A2 = (function() {
  class A {
    fn() {}
  }
  return A;
})();

let a1 = new A1();
let a2 = new A2();

log('a1 instanceof A1: ' + (a1 instanceof A1));
log('a1 instanceof A2: ' + (a1 instanceof A2));
log('a2 instanceof A1: ' + (a2 instanceof A1));
log('a2 instanceof A2: ' + (a2 instanceof A2));

function log(str) {
document.body.innerHTML += str + '<br>';
}