Fix the merge dropping the tail — find the bug

function merge(a, b) {
  const out = [];
  let i = 0, j = 0;
  while (i < a.length && j < b.length) {
    if (a[i] <= b[j]) out.push(a[i++]);
    else out.push(b[j++]);
  }
  return out;
}
document.querySelector('#out').textContent = merge([1, 3], [2, 4]).join("-");