When a client-side action needs to be validated from server-side, is it better to make the user wait or 'undo' the action if validation fails?

1. Which is better client-side validation or server-side validation?
2. Is it a good idea to validate form input on both the client-side and server-side?
3. Why is server-side validation recommended over client-side validation?
4. What are the advantages of validating data on the client-side before it is sent to the server?

Which is better client-side validation or server-side validation?

In general, it is best to perform input validation on both the client side and server side. Client-side input validation can help reduce server load and can prevent malicious users from submitting invalid data. However, client-side input validation is not a substitute for server-side input validation.

Is it a good idea to validate form input on both the client-side and server-side?

Your apps should always perform security checks on any form-submitted data on the server-side as well as the client-side, because client-side validation is too easy to bypass, so malicious users can still easily send bad data through to your server.

Why is server-side validation recommended over client-side validation?

Server-side validation is slower than client-side input validation. However, server-side input validation is more reliable than client-side input validation. Thus, it's safe to say that client-side data validation improves user experience while server-side input validation improves security.

What are the advantages of validating data on the client-side before it is sent to the server?

The advantages to using client-side validation are two-fold users receive feedback quicker (no need to go off to the server, process the information, then download another HTML page), and also it saves load on the server - more work is done on the client side.