universal_js_memoizer.js

function memoizer(fn) {
  if (typeof fn !== 'function') {
    console.error('Need a function.');
    return () => {};
  } else {
    return (() => {
      const cache = {};
      eval(`
        function memoized(...args) {
          const impl = ${fn.toString().replace('{', `{ const ${fn.name} = memoized; `)}
          const key = JSON.stringify(args);
          if (key in cache) {
            console.log('Using the value from the cache for args=' + key);
            return cache[key];
          } else {
            const r = impl(...args);
            cache[key] = r;
            return r;
          }
        };
      `);
      return memoized;
    })();
  }
}

// Demo `factorial(n)`.
function factorial(n) {
  console.log(`Computing factorial for N=${n}`);
  return n <= 0 ? 1 : n * factorial(n - 1);
}
const memoizedFactorial = memoizer(factorial);
console.log('First call to `factorial` to warm the cache.');
console.log(memoizedFactorial(5));
console.log('Next call to `factorial` to use the cache.');
console.log(memoizedFactorial(4));

// Demo `nchoosek(n,k)`, two arguments and define a function via `=>` instead.
// Note that it is using the cache even during the evaluation of the first, "warmup" call.
const nchoosek = (n, k) => {
  console.log(`Computing nchoosek for N=${n}, K=${k}`);
  if (k <= 0 || k >= n) {
    return 1;
  } else {
    return nchoosek(n-1, k) + nchoosek(n-1, k-1);
  }
};
const memoizedNchoosek = memoizer(nchoosek);
console.log('First call to `nchoosek` to warm the cache.');
console.log(memoizedNchoosek(5, 2));
console.log('Next call to `nchoosek` to use the cache.');
console.log(memoizedNchoosek(3, 1));

/*
First call to `factorial` to warm the cache.
Computing factorial for N=5
Computing factorial for N=4
Computing factorial for N=3
Computing factorial for N=2
Computing factorial for N=1
Computing factorial for N=0
120
Next call to `factorial` to use the cache.
Using the value from the cache for args=[4]
24
First call to `nchoosek` to warm the cache.
Computing nchoosek for N=5, K=2
Computing nchoosek for N=4, K=2
Computing nchoosek for N=3, K=2
Computing nchoosek for N=2, K=2
Computing nchoosek for N=2, K=1
Computing nchoosek for N=1, K=1
Computing nchoosek for N=1, K=0
Computing nchoosek for N=3, K=1
Using the value from the cache for args=[2,1]
Computing nchoosek for N=2, K=0
Computing nchoosek for N=4, K=1
Using the value from the cache for args=[3,1]
Computing nchoosek for N=3, K=0
10
Next call to `nchoosek` to use the cache.
Using the value from the cache for args=[3,1]
3
*/