Forms and validation

Forms are where users hand your app data, so they hold most of the frontend's logic. A controlled input keeps its value in state and updates it on every change. That makes live checking easy.

For bigger forms, a library such as React Hook Form cuts the repetitive code. Validate in the browser for fast feedback. Show the message next to the field, after the user leaves it or submits, not on every keystroke.

Disable the submit button while the request is running, so a double click does not create two records. Show errors from the server as clearly as your own. One rule matters for the rest of this roadmap: checks in the browser are for the user, checks on the server are for safety.