OPFS

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

The origin private file system (OPFS) is a storage endpoint provided as part of the File System API, which is private to the origin of the page and not visible to the user like the regular file system. It provides access to a special kind of file that is highly optimized for performance and offers in-place write access to its content.