I'm currently building out a multipage form using Flutter (frontend) and Node/Express/MongoDB/Mongoose (backend) for which I would like to implement auto-saving as the user progresses through each page (ie. clicking the next button after each page saves form data to the DB).

I have client-side validation to ensure fields are filled out and in the correct format, but I believe server-side validation is more important to implement in the event the user bypasses the client-side. I was wondering if anyone had general design ideas/processes I could implement for this idea. Some ideas I have:

  1. I'm thinking about sending a POST/PUT request to our server after each page, but I have no way of validating the incoming data server-side unless I create over 30 schemas for each of the pages. Each page has different questions so there isn't a single common validator I can use.

  2. Another option was having a temporary object with all the fields, and only validate the object at the very end when the user clicks 'submit,' but this is bad UX design in my mind as any error may require the user to be set back to the 1st or 2nd page which is frustrating for sure.

My main concern is validating the incoming data on the server-side as well as the client-side, but I can't seem to think of a good way to do both in a clean manner. I believe this question is language-agnostic, but I added my tech stack just in case.

Any help would be greatly appreciated :)