As others have said, client-side validation is to assist a user with providing proper values. (Example: Did you forget to type the "@" sign in your email? Did y

As others have said, client-side validation is to assist a user with providing proper values. (Example: Did you forget to type the "@" sign in your email? Did you miss a digit in your phone number?) But also, JS client-side validation is also client side, and therefore exposes the same amount of information to an adversary. Either way, you need input validation on the backend.