what is best js or php on form validation

Answer 1

I do Validate Forms from Server-side since users can't disable server-sided codes and can't see it.
But Client-side users can disable scripts or javascript which might be a major setback to site security.
But Ruben Perdigao Is Right
Validate from Frontend and Backend

Answer 2

both, you should always validate a form both the on front end and back end.