How to integrate new features demonstrations inside a JS app? [closed]

I'm looking for good practices concerning the integration of popover (or what so ever) tutorials, after deploying an update for example, to present new features to users (especially for a JS app, in my case with AngularJS).

A few questions to be more precise:

• How to ensure that the application and its tutorials remain independent? I mean, I guess tutorials' code shouldn't interfere with the app code. However, the tutorials need app code (maybe the router at least? Events?) to launch (or not). Would a "middleware" be the best choice?
• About tracing tutorials "cycle" (seen or not seen by the user), what would be the best between storing informations inside browser's API (localStorage for example) or on the server (database?)?
• Are tutorials a feature that needs to be anticipated before developping the app? Can't integrating it after the fact turn into a headache?
• Good practices on a UX point of view?