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.
The File and Directory Entries API simulates a local file system that web apps can navigate around. You can develop apps that can read, write, and create files and directories in a sandboxed, virtual file system. 
The FileSystemEntry interface of the File and Directory Entries API represents a single in a file system. The entry can be a file or a directory (directories are represented by the DirectoryEntry interface. It includes methods for working with files—including copying, moving, removing, and reading files—as well as information about a file it points to—including the file name and its path from the root to the entry.