const obj = { a: { b: null, getC: () => 42 } };
let calls = 0;
function sideEffect() {
  calls++;
  return 10;
}
const result = obj.a?.b?.getC?.() ?? sideEffect();
const result2 = obj.a?.z?.getC?.() ?? sideEffect();
console.log(result, result2, calls);

const counter = {
  count: 0,
  *[Symbol.iterator]() {
    yield this.count++;
    yield this.count++;
    yield this.count++;
  }
};

console.log([...counter], counter.count);

export {};