Fix the window recomputed each time — find the bug

const items = [2, 1, 5, 1, 3, 2];
let sum = 0;
for (let i = 0; i < 3; i++) sum += items[i];
let best = sum;
for (let i = 3; i < items.length; i++) {
  sum += items[i];
  best = Math.max(best, sum);
}
document.querySelector('#out').textContent = "best " + best;