indexedDB can easily store gigabytes of data without issue. I've personally used it to do so before, and it will happily "cache" it for weeks at a time. There are several web apps which work entirely offline and cache all of their data using that API.

devdocs.io is one of them.

Like the parent commenter said, i'd welcome more control over the storage of that data, but it absolutely can and will cache large blobs like that.