IndexedDB

IndexedDB provides a robust transactional database system within the browser, moving beyond the 5MB limits of localStorage to handle gigabytes of data. It operates on an object-oriented model rather than relational tables: you store JavaScript objects indexed with a key. This asynchronous API supports high-performance searches using indexes and allows web applications to function reliably offline. Developers use it to cache application state, manage large datasets for PWAs, and sync local changes back to a server once a connection restores.

https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API