I’d still consider avoiding clientside validations because development costs, and a standard javascript library for validations would keep development costs low. The standard library would also reduce browser issues with client-side code. (of course there could be browser issues with AJAX as well, but the more javascript, the more browser problems, and the higher development costs.)

Furthermore, client-side validations — library or not — will result in validations two places: I must maintain validations both client-side and server-side. Increased maintanence costs.

You could say the arguments above are mostly related to cost or development time. And I think it’s important also to address usability issues. As Yoink points out, network issues could result in slow responses rendering AJAX validations unusable. This could alter the equation.

However, there is one very important issue: Using both client-side and AJAX validations, how would you ensure a consistent user interface? In my opinion, if you choose both validations, you could easily end up putting a lot of effort into making the two types of validations work consistently.

Which fields should be validated client-side? Which should validate server-side AJAX style? Which fields should use both validations? What should happen if a field validates OK in javascript, but then fails the AJAX validations? Any cross-field validations? What if an AJAX validation fails and then the user corrects the value but makes a typo? Next validation of the field might result in OK javascript validation, but failed AJAX validation. When exactly should the field change from OK to failed and what would you do to prevent the client-side validation, when the result really does not validate?

As you see, lots of considerations. and I haven’t found a generic cross-browser framework that handles these considerations yet. (If you know of one, please let me know!)

Having said that, I’ll give fValidate a closer look to see what it’s capable of. Only one problem, though: I spend an hour googling for a download file of fValidate, but couldn’t find it. It seems that the original URL is not working (www.peterbailey.net). Anybody knows a download link?

Accessability support is mainly provided by OS’s, and for a small part by the application itself.

So if accessability should be supported in a standard way, there should be a supporting application for all RIA platforms, like Ajax and Macromedia Flex, Microsoft Vista etc.

Hopefully this standard will develop…

S!d

So it could be that it was a bit more cost efficient to develop only server-side validation via Ajax than use your three step validation (which is in my opinion technically the best one). The costs here are probably moved to the bandwidth and server usage for the validations which fail and could be done on the client.

S!d