This is a difficult question to answer in the abstract, but in general everything that is not directly involved with user interaction - including what sounds like making “processed data” and timers - belongs IMHO in a service provider, not a page.
Hopefully that’s all the information you need, because now there are no longer functions attached to pages that you have to worry about.
Incidentally, “local storage” is a very overloaded term. If you are really strictly speaking about this thing, it’s never the right choice for anything. Ionic Storage offers an almost identical API and better persistence guarantees.
At this point, it would probably help to know what the “data processing” consists of. If it’s a long-running and pausable task that can be easily broken into chunks (think bitcoin mining), then it might make sense to use some sort of device storage to allow the app to get paused and resumed while the work is ongoing. In virtually any other scenario, such as modifying a student record retrieved from a network API by enrolling them in a class or changing their legal name, you do not want to use on-device storage here at all. It’s a bad choice for in-app communication because you have to concern yourself with sequencing writes and reads, which is a very tedious and error-prone process.