Travis build: 768 [ci skip]

README.md

@@ -273,6 +273,7 @@
 <summary>View contents</summary>
 
 * [`join`](#join)
+* [`mask`](#mask)
 * [`sortedIndex`](#sortedindex)
 
 </details>
@@ -4619,6 +4620,30 @@ join(['pen', 'pineapple', 'apple', 'pen']); //"pen,pineapple,apple,pen"
 <br>[⬆ back to top](#table-of-contents)
 
 
+### mask
+
+Replaces all but the last `num` of characters with the specified mask character.
+
+Use `String.slice()` to grab the portion of the characters that need to be masked and use `String.replace()` with a regex to replace every character with the mask character. 
+Concatenate the masked characters with the remaining unmasked portion of the string.
+Omit the second argument, `num`, to keep a default of `4` characters unmasked.
+Omit the third argument, `mask`, to use a default character of `'*'` for the mask.
+
+```js
+const mask = (cc, num = 4, mask = '*') =>
+  ('' + cc).slice(0, -num).replace(/./g, mask) + ('' + cc).slice(-num);
+```
+
+```js
+mask(1234567890); // '******7890'
+mask(1234567890, 3); // '*******890'
+mask(1234567890, 4, '$'); // '$$$$$$7890'
+mask(1234567890, -4, '$'); // '1234$$$$$$'
+```
+
+<br>[⬆ back to top](#table-of-contents)
+
+
 ### sortedIndex
 
 Returns the lowest index at which value should be inserted into array in order to maintain its sort order.