add mask

snippets/mask.md

@@ -0,0 +1,15 @@
+### mask
+
+It replace all but the last(first if `num` is negative) `num` (by default it is 4) characters by the provided mask(`'*'` by default).
+
+```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,'$') // '$$$$$$7890'
+mask(1234567890,-4,'$') // '1234$$$$$$'
+```