Design a better validation experience for MVC

[danroth27]

#8573 (comment) covers the problem statement for this issue

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Bootstrap 5 is removing it's dependency on jQuery: twbs/bootstrap#23586

This issue tracks investigating what removing jQuery as a dependency from ASP.NET Core would take.

We're going to split this work into two phases:

1. Design the new JS library to replace jquery-validation-unobstrusive
2. Implement the above
3. HTMLHelper default css class names #17412

[mkArtakMSFT]

@ryanbrandenburg can you please investigate and come up with some cost for this work? Thanks!

[mkArtakMSFT]

@danroth27 seems we rely on jQuery for our validation too, it's not just transitive because of Bootstrap dependency.

[danroth27]

@mkArtakMSFT Right, the main work item tracked by this issue is investigating what it would take to remove the jQuery dependency from our validation support.

[danroth27]

Given that our current validation support is built on jQuery validation, the way I would think about this issue is to take a fresh look at what our client validation support should look like. Is there a different validation library that we should consider using? Etc.

[ryanbrandenburg]

The one option that seems to be most popular (and standards compliant) would be using the built-in HTML5 form validation. The problem there is that it would only work for client-side validation. As far as I can tell HTML5 form validation doesn't solve any server-side validation problems, and even if it did it would require a lot of changes to DataAnnotations. HTML5 also isn't supported on older browsers (IE9 was the example I found).

In my opinion it's not worth the work that would be required to remove our dependencies here in the absence of a more unified vision about what value we can produce from re-working DataAnnotations.