Origin private file system (OPFS)

Carlo Francisco gave a ~15m talk a couple days ago at the Browsertech WASM event in NYC (~7:30 to 23:50) covering Notion's use of WASM SQLite in the browser. In it he explained the Origin private file system, or OPFS (among other neat stuff like SharedWorkers and cross-origin isolation).

TL;DR on OPFS: your website gets read+write access to local files on a user's device, but the user can't see the files.

Per MDN:

[OPFS] is a storage endpoint provided as part of the File System API...OPFS offers low-level, byte-by-byte file access, which is private to the origin of the page and not visible to the user.

More on OPFS

• The regular File System API trades speed for security whereas OPFS can run faster since it's private to the origin and not user-visible
• Synchronous file access via OPFS must run in a Web Worker to avoid blocking the main thread
• Since OPFS is a browser storage mechanism (like IndexedDB), it has a storage quota, and clearing site data clears OPFS
• (Per Carlo) OPFS doesn’t handle concurrency between tabs gracefully, so you have to do it yourself (e.g. use a SharedWorker for a single db connection).