simpler solution to mask using padStart

snippets/mask.md

@@ -2,14 +2,13 @@
 
 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 regexp to replace every character with the mask character.
+Use `String.slice()` to grab the portion of the characters that will remain unmasked and use `String.padStart()` to fill the beginning of the string with the mask character up to the original length.
-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. If `num` is negative, the unmasked characters will be at the start of the string.
 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);
+  ('' + cc).slice(-num).padStart(('' + cc).length, mask);
 ```
 
 ```js

test/mask/mask.js

@@ -1,3 +1,3 @@
 const mask = (cc, num = 4, mask = '*') =>
-  ('' + cc).slice(0, -num).replace(/./g, mask) + ('' + cc).slice(-num);
+  ('' + cc).slice(-num).padStart(('' + cc).length, mask);
 module.exports = mask;