I have a use case for synchronous storage for my react native app.
Before app renders a home view, I want to check if there is a session token stored on the local storage and proceed if it is available, otherwise want to render login component instead as the initial view.
Using sync storage will simplify the code.
I don't think there is a simple synchronous storage option. According to this answer localstorage is not implemented in the core IOS javascript engine. AFAIK the other options such as those used in this localstorage polyfill don't work. That leaves us with needing a react native module which are asynchonous by design. From the docs:
React Native bridge is asynchronous, so the only way to pass a result to JavaScript is by using callbacks or emitting events
So I think Async is the way to go.