File and Directory Entries API - Web APIs 编辑

Non-standard

This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

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.

Because this is a non-standard API, whose specification is not currently on a standards track, it's important to keep in mind that not all browsers implement it, and those that do may implement only small portions of it. Check the Browser compatibility section for details.

Two very similar APIs exist depending on whether you desire asynchronous or synchronous behavior. The synchronous API is intended 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.

The Firefox implementation of the File and Directory Entries API is very limited; there is no support for creating files. Only for accessing files which are selected by the user in a file <input> element (see HTMLInputElement as well) or when a file or directory is provided to the Web site or app using drag and drop. Firefox also does not implement the synchronous API. Check the browser compatibility for any part of the API you use carefully, and see File and Directory Entries API support in Firefox for more details.

Getting access to a file system

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

• When handling a drop event for drag and drop, you can call DataTransferItem.webkitGetAsEntry() to get the FileSystemEntry 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 property lets you access the FileSystemFileEntry objects for the currently selected files, but only if they are dragged-and-dropped onto the file chooser (bug 1326031). If HTMLInputElement.webkitdirectory is true, the <input> element is instead a directory picker, and you get FileSystemDirectoryEntry objects for each selected directory.

Asynchronous API

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

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

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

FileSystemFlags

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().

Synchronous API

The synchronous API is should only be used in Workers; these calls block until they're finished executing, and 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().

Other Interfaces

LocalFileSystem

Gives you access to a sandboxed file system.

LocalFileSystemSync

LockedFile

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

Metadata

Specifications

Specification	Status	Comment
File and Directory Entries API	Draft	Draft of proposed API

This API has no official W3C or WHATWG specification.

Browser compatibility

FileSystem

BCD tables only load in the browser

FileSystemSync property

BCD tables only load in the browser

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Introduction to the File and Directory Entries API
• File and Directory Entries API support in Firefox