File and Directory Entries API

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 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 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. 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.
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: 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().

Specifications

Specification	Status	Comment
File and Directory Entries API	Editor's Draft	Draft of proposed API

This API has no official W3C or WHATWG specification.

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari
Asynchronous API	13 webkit	50 (50)^[1]	No support	No support	No support
Synchronous API	13 webkit	No support	No support	No support	No support

Feature	Android	Chrome for Android	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Asynchronous API	No support	(Yes) webkit	50.0 (50)^[1]	No support	No support	No support
Synchronous API	No support	(Yes) webkit	No support	No support	No support	No support

[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.