How do I bundle a service worker, as suggested in the guide "Session management with service workers"

[ben519]

I'm following the guide Session management with service workers. Currently I'm getting the error

Cannot use import statement outside a module (at service-worker.js:1:1)

I suspect it's related to this note in the guide

Make sure that the service worker is bundled so that it will still work after the browser has been closed.

Can anyone guide me on how to bundle a service worker using Next.js? This feels like a significant step that is glossed over, and I'm quite lost.

Thanks!