Update memoize to use a map and allow access to it

snippets/memoize.md

@@ -2,13 +2,16 @@
 
 Returns the memoized (cached) function.
 
-Use `Object.create(null)` to create an empty object without `Object.prototype` (so that those properties are not resolved if the input value is something like `'hasOwnProperty'`).
+Create an empty cache using by instantiating a new `Map` object.
 Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not.
+Allow access to the `cache` by setting it as a property on the returned function.
 
 ```js
 const memoize = fn => {
-  const cache = Object.create(null);
-  return value => cache[value] || (cache[value] = fn(value));
+  const cache = new Map();
+  const cached = val => cache.get(val) || (cache.set(val, fn(val))) && cache.get(val);
+  cached.cache = cache;
+  return cached;
 };
 ```
 
@@ -17,4 +20,5 @@ const memoize = fn => {
 const anagramsCached = memoize(anagrams);
 anagramsCached('javascript'); // takes a long time
 anagramsCached('javascript'); // returns virtually instantly since it's now cached
+console.log(anagramsCached.cache); // Map
 ```