What if there is no internet connection?
Offline mode if possible in PWA
The capability to work offline is one of the key values that separates a PWA application from a web site. You can read on what is PWA and mPWA over here. In general most of native apps these days can not fully function without the internet. Meaning that either data exchange is awlays on or it happends at some relatvely longer intervals. Offline behaviour depends on the operating system and it's version, generally Android provides for more capabilities coparng to iOS, howver that gap has been lately closing .
Offline without a download?
Even though there is no visible app download and installation on user's part, still data is received from the internet. We can manage what data stays on the smartphone with a simple set of settings in the Mobsted App maker. Please refer to the _Setting up an offline mode article_. Mobsted does offline storage automatically, which is specific for speed of user interfaces, but if you want the app to work offline, like store data and perform some actions you will need to pay attention to setting up the offline mode.
So - a progressive web app can functions without an internet connection and save data, despite that it was not downloaded to user's phone. For example, if you choose PWA technology for an app for your employees to inspect communication equipment in building's basements, it is likely there could be no internet connection. User will still be able to save data and take photos and so on, and it will be synced when back on the internet.
How is it synced?
The behaviour depends on the operating system. In most newer Android version every time you phone detects online connection the sync happens automatically in the backroad. In anything up to the current version of iOS (11) user will need to have the app opened to sync data. However with the release of Service Workers in iOS/Safari it is expected that sync could happen in background. In both cases the app saves what ever is necessary even when no internet connection is there.
Making PWA work without the internet is relatively easy when using a platform with such functions and the platform does take care of all the possible combinations of operating systems. Still if you need some heavy logic or calculations working offline, PWA might not fit your needs.