For small changes like adding a field, we make the property on the underlying event optional, but require it in the event dispatch function. That allows old events to be missing the field, but type-checking still requires it in the codebase going forward. It does require a special case to handle the missing field, however.

For larger changes to events, we do migrations. We store events in Postgres, so we just use TypeORM migrations. I haven’t had to do one of these myself, but I’ve heard secondhand that it’s not too bad. We don’t have very many of these, regardless.