Add mapValues, mapKeys

snippets/mapKeys.md

@@ -0,0 +1,15 @@
+### mapKeys
+
+Creates an object with keys generated by running the provided function for each key and the same values as the provided object.
+
+Use `Object.keys(obj)` to iterate over the object's keys.
+Use `Array.reduce()` to create a new object with the same values and mapped keys using `fn`.
+
+```js
+const mapKeys = (obj, fn) =>
+  Object.keys(obj).reduce((acc,k) => {acc[fn(obj[k], k, obj)] = obj[k]; return acc;},{});
+```
+
+```js
+mapKeys({ 'a': 1, 'b': 2 }, (val, key) => key + val); // { a1: 1, b2: 2 }
+```