Add mapString, fix dig

snippets/dig.md

@@ -5,7 +5,7 @@ Returns the target value in a nested JSON object, based on the given key.
 Use the `in` operator to check if `target` exists in `obj`.
 If found, return the value of `obj[target]`, otherwise use `Object.values(obj)` and `Array.reduce()` to recursively call `dig` on each nested object until the first matching key/value pair is found.
 
-```
+```js
 const dig = (obj, target) =>
   target in obj
     ? obj[target]
@@ -17,7 +17,7 @@ const dig = (obj, target) =>
         }, undefined);
 ```
 
-```
+```js
 const data = {
   level1:{
     level2:{

snippets/mapString.md

@@ -0,0 +1,16 @@
+### mapString
+
+Creates a new string with the results of calling a provided function on every character in the calling string.
+
+Use `String.split('')` and `Array.map()` to call the provided function, `fn`, for each character in `str`.
+Use `Array.join('')` to recombine the array of characters into a string.
+The callback function, `fn`, takes three arguments (the current character, the index of the current character and the string `mapString` was called upon).
+
+```js
+const mapString = (str, fn) =>
+	str.split('').map((c, i) => fn(c, i, str)).join('');
+```
+
+```js
+mapString('lorem ipsum', c => c.toUpperCase()); // 'LOREM IPSUM'
+```