In the File System API, a FileException object represents error conditions that you might encounter while accessing the file system using the synchronous API. It extends the FileException interface described in File Writer and adds several new error codes.
In the File System API, a FileSystemSync object represents a file system. It has two properties.
The LocalFileSystem interface of the File System API gives you access to a sandboxed file system.  The methods are implemented by window and worker objects.
The LocalFileSystemSync interface of the File System API gives you access to a sandboxed file system. It is intended to be used with WebWorkers. The methods are implemented by worker objects.