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 (en-US) 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 (en-US)event for drag and drop, you can callDataTransferItem.webkitGetAsEntry()(en-US) to get theFileSystemEntry(en-US) for a dropped item. If the result isn'tnull, then it's a dropped file or directory, and you can use file system calls to work with it. - The
HTMLInputElement.webkitEntriesproperty lets you access theFileSystemFileEntryobjects for the currently selected files, but only if they are dragged-and-dropped onto the file chooser (バグ 1326031). IfHTMLInputElement.webkitdirectoryistrue, the<input>element is instead a directory picker, and you getFileSystemDirectoryEntryobjects 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(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().
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(en-US)- 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.
LocalFileSystemSyncLockedFile(en-US)- Provides tools to deal with a given file with all the necessary locks.
Metadata(en-US) Experimental
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.