Ah okay - I'm guessing that the system I was looking at logged the click, then. 
How are you currently utilizing localStorage? Ultimately, the sandboxing we currently do for custom domains prevents the app from hitting any browser APIs, meaning the most direct replacement would probably be RetoolDB.
Have you previously expressed interest in the Retool CLI? I can probably get you access, as that would definitely be the cleanest way to get this done until we enable file creation via the UI.