File and Directory Entries API

非標準

この機能は標準ではなく、標準化の予定もありません。公開されているウェブサイトには使用しないでください。ユーザーによっては使用できないことがあります。実装ごとに大きな差があることもあり、将来は振る舞いが変わるかもしれません。

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 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.

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:

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 (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  これは廃止された API であり、動作は保証されていません。
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 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  これは廃止された API であり、動作は保証されていません。
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 (en-US)
Provides tools to deal with a given file with all the necessary locks.
Metadata (en-US) これは実験段階の API です。製品内のコードで使用しないようご注意ください。

Specifications

Specification Status Comment
File and Directory Entries API ドラフト Draft of proposed API

This API has no official W3C or WHATWG specification.

Browser compatibility

FileSystem

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FileSystemSync property

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See also