Where do you record validation rules for form data in a web application?

Question

Say you have a web form with some fields that you want to validate to be only some subset of alphanumeric, a minimum or maximum length etc.

You can validate in the c

Answer 1

As others have said, you need to validate on the server side for security and data-integrity reasons, and validating on the client-side will improve the user experience, since users will have a chance to fix their mistakes sooner.

It seemed the question was asking more about how do you define the validations so every place that validates is in sync. I would recommend defining your validation rules in one place, such as an XML file, or something, and having a framework that reads that file, and generates javascript functions to validate on the client. It can then use the same rules to validate on the server.

This way, if you ever need to change a rule, you have one place to go.