If you don't want to use a framework, it means "Vanilla JavaScript". You really don't need any framework to do fetch()+FormData API (AJAX) calls to your Node backend, however, on backend, I would recommend using at least Express. It's very lightweight http library on the top of of Node API.
Yes, Vanilla JS in frontend is very common in production and I use it often as well.
Here is my article which might give you some tips on how you can do Vanilla JS components without any frameworks.