> What is ajax Server-side validation relying on JavaScript. You still have to wait for the server to respond, and now you need to implement UI to tell the use

> What is ajax Server-side validation relying on JavaScript. You still have to wait for the server to respond, and now you need to implement UI to tell the user something is happening in the background. But at least you can start proactively validating before the user actually submits the form, so there's that.