Have you looked into webassembly and how browsers give access to filesystems[1], there could be hope for a future of high performant filesystem access.
This interface will not grant you access to the users filesystem. Instead you will have a "virtual drive" within the browser sandbox. If you want to gain access to the users filesystem you need to invoke the user by eg. installing a Chrome extension. The relevant Chrome API can be found here.
If you are accessing the file system, you are accessing an abstraction, not the actual disk data (which is another abstraction on top of the actual hardware).
[1] https://developer.mozilla.org/en-US/docs/Web/API/FileSystem