When answering this interview question, you should demonstrate your understanding of how form validation works both on the client side and the server side. Here's an example of how you could answer this question:
On the server side, I would also perform validation to ensure that the data submitted by the user is valid and secure. This would include validating data types, checking for SQL injection attacks, and making sure that any uploaded files are safe to use. I would also make sure to sanitize any input to prevent cross-site scripting attacks.
In general, I would try to use both client-side and server-side validation to provide a more robust and secure form submission process. By using client-side validation, I can provide immediate feedback to the user, while server-side validation can catch any errors that may have been missed or intentionally bypassed by the client.