function memoize(fn) {
  const cache = new Map();
  return (...args) => {
    const key = JSON.stringify(args);
    if (cache.has(key)) return cache.get(key);
    const result = fn(...args);
    cache.set(key, result);
    return result;
  };
}

let calls = 0;
const add = memoize((a, b) => { calls++; return a + b; });

const r1 = add(1, 2);
const r2 = add(2, 1);
const r3 = add(1, 2);
console.log(r1, r2, r3, calls);