File and Directory Entries API

The File and Directory Entries API simulates a local file system that web apps can navigate within and access files in. You can develop apps which read, write, and create files and/or directories in a virtual, sandboxed file system.

Two very similar APIs exist depending on whether you desire asynchronous or synchronous behavior. The synchronous API is indended to be used inside a Worker and will return the values you desire. The asynchronous API will not block and functions and the API will not return values; instead, you will need to supply a callback function to handle the response whenever it arrives.

There are two ways to get access to file systems defined in the current specification draft:

• When handling a drop (en-US) event for drag and drop, you can call DataTransferItem.webkitGetAsEntry() (en-US) to get the FileSystemEntry (en-US) for a dropped item. If the result isn't null, then it's a dropped file or directory, and you can use file system calls to work with it.
• The HTMLInputElement.webkitEntries (en-US) property lets you access the FileSystemFileEntry objects for the currently selected files, but only if they are dragged-and-dropped onto the file chooser (バグ 1326031). If HTMLInputElement.webkitdirectory is true, the <input> element is instead a directory picker, and you get FileSystemDirectoryEntry objects for each selected directory.

The asynchronous API should be used for most operations, to prevent file system accesses from blocking the entire browser if used on the main thread. It includes the following interfaces:

FileSystem

Represents a file system.

FileSystemEntry (en-US)

The basic interface representing a single entry in a file system. This is implemented by other interfaces which represent files or directories.

FileSystemFileEntry

Represents a single file in a file system.

FileSystemDirectoryEntry

Represents a single directory in a file system.

FileSystemDirectoryReader (en-US)

Created by calling FileSystemDirectoryEntry.createReader() (en-US), this interface provides the functionality which lets you read the contents of a directory.

FileSystemFlags (en-US)

Defines a set of values which are used when specifying option flags when calling certain methods in the File and Directory Entries API.

FileError 

Represents an error which is generated by asynchronous file system calls.

There are also two global functions (which are not part of the specification at this time and are implemented only by Google Chrome). They're available on the Window object and implemented in LocalFileSystem: requestFileSystem() and resolveLocalFileSystemURL().

The synchronous API is should only be used in Workers; these calls block until they're finished executing, and simply return the results instead of using callbacks. Using them on the main thread will block the browser, which is naughty. The interfaces below otherwise mirror the ones from the asynchronous API.

FileSystemSync

Represents a file system.

FileSystemEntrySync

The basic interface representing a single entry in a file system. This is implemented by other interfaces which represent files or directories.

FileSystemFileEntrySync

Represents a single file in a file system.

FileSystemDirectoryEntrySync

Represents a single directory in a file system.

FileSystemDirectoryReaderSync

Created by calling FileSystemDirectoryEntrySync.createReader(), this interface provides the functionality which lets you read the contents of a directory.

FileException 

Represents an error which is generated by synchronous file system calls.

There are also two global functions (which are not part of the specification at this time and are implemented only by Google Chrome). They're available on the Worker object and implemented in LocalFileSystemSync: requestFileSystemSync() and resolveLocalFileSystemSyncURL().

LocalFileSystem

Gives you access to a sandboxed file system.

LocalFileSystemSync

 

LockedFile (en-US)

Provides tools to deal with a given file with all the necessary locks.

Metadata (en-US)

This API has no official W3C or WHATWG specification.

• Introduction to the File and Directory Entries API
• File and Directory Entries API support in Firefox (en-US)