Функция запоминания

const memoize = fn => {
  const cache = new Map();
  const cached = function (val) {
    return cache.has(val)
      ? cache.get(val)
      : cache.set(val, fn.call(this, val)) && cache.get(val);
  };
  cached.cache = cache;
  return cached;
};

// See the `anagrams` snippet.
const anagramsCached = memoize(anagrams);
anagramsCached('javascript'); // takes a long time
anagramsCached('javascript'); // returns virtually instantly since it's cached
console.log(anagramsCached.cache); // The cached anagrams map