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非标准
该特性是非标准的，请尽量不要在生产环境中使用它！
文件和目录条目API模拟一个web应用可以导航和访问的本地文件系统. 你在虚拟的沙箱文件系统中可以开发一个读, 写, 创建文件或者目录的应用.
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:
- When handling a
dropevent for drag and drop, you can callDataTransferItem.webkitGetAsEntry()to get theFileSystemEntryfor 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 (bug 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- 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 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.
EntrySync 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.
LocalFileSystemSyncLockedFile- 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
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Asynchronous API | 13 webkit | 50 (50)[1] | 未实现 | 未实现 | 未实现 |
| Synchronous API | 13 webkit | 未实现 | 未实现 | 未实现 | 未实现 |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Asynchronous API | 未实现 | (Yes) webkit | 50.0 (50)[1] | 未实现 | 未实现 | 未实现 |
| Synchronous API | 未实现 | (Yes) webkit | 未实现 | 未实现 | 未实现 | 未实现 |
[1] Firefox 50 introduces partial support for the File and Directory Entries API. Be sure to check the compatibility tables for individual interfaces and methods before using them, to ensure that they're supported, before you use them. The API can be disabled by setting the value of the preference dom.webkitBlink.filesystem.enabled to false.