Add memoize snippet

snippets/memoize.md

@@ -0,0 +1,23 @@
+### memoize
+
+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').
+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.
+
+```js
+const memoize = fn => {
+  const cache = Object.create(null);
+  return value => cache[value] || (cache[value] = fn(value));
+};
+```
+
+```js
+// See the `anagrams` snippet.
+const anagramsCached = memoize(anagrams);
+anagramsCached('javascript'); // takes a long time
+anagramsCached('javascript'); // returns virtually instantly since it's now cached
+```