A WebWorker can free up the main thread so the UI doesn't grind to a halt. Unfortunately they might not help you here. Data in/out of the worker is string only[0], so the extra parsing/serializing usually ruins any perf benefit.

You can access indexedDB from the worker, though. So you load the DB from the main thread, then you can do the filtering from the worker. You could return indexes then fetch those from indexDB on the main thread.

None of this will help with parsing large strings though, you are probably stuck with doing that on the main thread. And it is also not going to reduce the total time to perform the work. But hopefully it will avoid pinning the main thread, because that is bad.

I really enjoy this stuff, so feel free to contact me if you wanna talk it through. My email address is in my profile.

[0] SharedArrayBuffers were recently re-enabled according to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...