Is JavaScript validation bad?

Is JavaScript validation worth of it?

Yes, as it provides a better user experience and preserves bandwidth.

Should we ever use it now?

Yes, for the aforementioned reasons.

Are there any solutions to this?

Yes, use server-side validation as well.

What if the user (or probably a bad guy) disables javascript?

As said before: Simply do not rely on the client. Never do so. Check everything on the server again.

Should we ever use it now?

Yes - so the user immediately sees what's wrong. Otherwise he had to post back the data first which may take a while. By the way you reduce traffic to your server.

It's simply more inuitive.

//EDIT: BTW: The ASP.NET ValidationRules contain both client-side and server validation as far as I know.

Javascript validation is good because it provides a better user experience.

You should however never rely on it and should validate on the server regardless.

If you're looking to save time, go with server-side only. If you want better performance and user experience, add client-side validation afterward. Never rely on client-side validation, for the reasons you state. All critical validation should occur on the server ... even if duplicated on the client.

Using JavaScript is not wrong. We've been using it since a long time. It is used for applying client-side validations.

Still, we should implement server-side validation so that a bad guy would not be able to break the application.

Client-side (Javascript) validation is about usability, nothing else. If the cost of implementing is not worth the perceived increase in usability, then don't spend the time on it. These days it's pretty easy to do though!

I don't think you can do without server-side validation, however, since this is the only thing that provides you with any security.

JavaScript is useful for client side validation. But you cannot rely only on them. You must use server-side validation against the posted data. JavaScript just prevents unnecessary posts to the server.

In a multi-tiered / service orientated environment validation should exist on multiple levels to allow for better reuse while still maintaining a secure application. Validation on the client side, whether in a desktop app, or web site/application should be there for a better user experience to prevent postbacks to the server everytime for validation, hence costing more bandwidth and user time. If client-side validation cannot be moved entirely to the front end then consider using ajax for a partial postback to a server side validation routine, while retaining a better customer experience but allowing a programmer to maintain the validation rules centrally.

Second to the client side, but more importantly, server side code should validate the data before persisting it via a data layer or passing it to another server side method/service, to employ business rules around the data and help prevent errors in data integrity. Lastly, the persistence layer itself (the immediate interface to the database or other storage mechanism) should validate the data being stored, again to prevent errors in data integrity and possibly further business rules. The last thing you want is a data store with useless data.

Employing this method will keep you data secure and integrity in line. On reuse of either you persistence layer, your data layer or your front-end presentation thereafter, in your own site (or via a web service, desktop application or mobile app), if designed properly, these validation routines are already in place and can be re-employed. This should prove to be of great benefit to you alone, and your colleagues and your management, if you happen work in a team.

Javascript is a client-side scripting language. Therefore we can use client-side validations by using it. It helps to reduce the load that goes to the server-side. That's why js validation is worthy. And that is the reason for use it for client-side validations. But we should not only depend on js validations. Because the client can turn off the js engine at any time. If so, it causes a big problem.