const obj = { a: { b: null }, getVal: null };
let counter = 0;
function sideEffect() {
  counter++;
  return counter;
}
const result = obj?.a?.b?.[sideEffect()] ?? 'default1';
const result2 = obj.getVal?.(sideEffect()) ?? 'default2';
const result3 = obj?.a?.c?.d ?? sideEffect();
console.log(result, result2, result3, counter);