Fix the cache never checked — find the bug

function memoize(fn) {
  const cache = new Map();
  return function (n) {
    const result = fn(n);
    cache.set(n, result);
    return result;
  };
}
let calls = 0;
const double = memoize(function (n) { calls++; return n * 2; });
double(5);
double(5);
document.querySelector('#out').textContent = String(calls);