Is there any way to check a field against Regex as a user is typing in Velocity?

I'm trying to get some code working in DotCMS that will check as a user types against Regex (for password validation). I already have the Regex sorted but i can't find any way to do a positive look ahead on the field as the user types.

The only way I can think to make this happen is by creating a custom field. That way, you can make it act exactly how you would like it to act.