class Money {
  #amount;
  constructor(amount) { this.#amount = amount; }
  [Symbol.toPrimitive](hint) {
    if (hint === 'number') return this.#amount;
    if (hint === 'string') return `$${this.#amount}`;
    return `Money(${this.#amount})`;
  }
}
const m = new Money(42);
console.log(`${m}`, m + 8, m == 42);

const arr = [1, 2, 3, 4, 5];
arr[Symbol.iterator] = function* () {
  for (let i = 0; i < 3; i++) yield arr[i] * 2;
};
console.log([...arr], JSON.stringify(arr));

function test() {
  try {
    console.log(y);
  } catch (e) {
    return e.constructor.name;
  }
}

let result1 = test();
let y = 'hoisted';

console.log(result1, typeof y, y);

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);