What is best practices in storing server content on webpage?

Iim not really a webdeveloper, but im kinda pushed into a situation.

When serverAPI returns JSON data to an iOS app for example, the app would store things like userID, cityID & stateID etc so that it can return those values back to the server if changes occur client side.

Where do we store those variables on webpages.. is it in:

1. hidden input fields?
2. JavaScript?
3. something else?

I am only trying to store about 6-7 variables. What is the best practice in this use case? I did google, but they were giving me either more complex information or irrelevant once used the keyword webpage and javascript