OPFS

A high-performance, browser-side virtual file system designed for private, sandboxed storage with native-level I/O speeds.

The Origin Private File System (OPFS) provides a dedicated storage endpoint for web applications that bypasses the latency of traditional IndexedDB or LocalStorage. By leveraging the FileSystemSyncAccessHandle (available in Web Workers), developers achieve synchronous, low-level read and write operations on local bytes. It is the standard choice for heavy-duty workloads like SQLite's Wasm implementation, Photoshop on the web, and large-scale video editing. OPFS ensures data isolation by anchoring storage to the site's origin: ensuring that while the browser manages the disk space, the user's operating system remains shielded from direct file access.

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