Well, for my latest iteration, I'm using Bun+Elysia on the server which uses Typebox for request validation+schema, which is effectively JSON Schema so you could do something similar in other languages. I can pass that schema down to the client/browser, and I could use AJV to run that schema against the request before I send it to the server, but there's a couple tricky parts.
1.Json schema/AJV return not very human friendly results and they're hard to associate with a specific field to display the error nicely
2. If you want to validation as the user is typing to clear errors as they're satisfied, you have to run the entire schema, not just for that one field
3. Any async validations like checking if a username is unique is harder if not impossible with this approach
