IndexedDB

IndexedDB stores JavaScript objects (files and blobs included) in object stores with indexes, inside the browser and separately for each website. It holds far more than localStorage, often hundreds of megabytes or more depending on the browser and free disk space, and it never freezes the page because every operation is asynchronous.

Its raw API is event-based and clumsy, so most apps use a wrapper such as Dexie.js or idb. Data stays in that one browser on that one device; syncing it anywhere else is up to the app. Browsers may clear it when storage runs low unless the site asks for persistent storage.