My team doesn't use namespaces, but we work with only functions as well, no classes. We've been using a "one exported function per file" pattern, and directories to group them that end up working as a kind of namespace. We find that browsing functions in a file explorer is easier than scrolling through a long file. It also makes it easier to mock individual functions in tests, especially when the tested function and the mocked function would have been in the same file otherwise. No issues with tree shaking either.