I am making a todo app with Javascript (PWA). There will be reminders for the todos. I want to send notifications to the user to remind them. Tasks and remind time will be stored in localStorage.

So now I want to send push notifications without any backend. I have tried some tutorials, they all require a backend or Google push services for it. Is there any way to push notifications without them? I think the serviceWorker have to keep running in the background and get the current time. Remind the user if current time and remind time matches. So how to do it?