```javascript
> moment = require('moment');
> moment('121314', 'MMDDYY').isValid();
true
> moment('121314', 'MMDDYY').format();
'2014-12-13T00:00:00+02:00'
> moment('141312', 'MMDDYY').isValid();
false
> moment('141312', 'MMDDYY').format();
'Invalid date'
```