Handling Background Tasks & Services

Ten deliveries are finished in a basement with no signal, and then the courier locks the phone and walks back to the van. The app recorded every delivery, but the server has none of them, and the courier will not open the app again for an hour. Those records should reach the server without the courier doing anything, and that requires code that runs when the app is not on the screen.

Work like this is called a background task. You cannot simply keep a timer running to do it. Shortly after an app leaves the screen, the operating system suspends it to save battery, and a `setInterval