Is JavaScript validation better than server side validations?

Answer 1

Server side validation is your final line of defense and should not be neglected.

And as Mirielle indicated, a user may be able to bypass validations by tinkering with the client code (editing html tags properties in developer console for instance)

For better user experience it's best to also implement client side validation as well (invalid input indication, missing inputs, etc...)

You can also minimize calls to the server by preventing requests before the input is valid.

Answer 2

Server side validation is a must.

Frontend validation is optional.

Answer 3

client side validation can be changed by user scripts injection with something like Greasemonkey.