LocalFileSystem

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基本概念
方法概述
常量
方法
浏览器兼容性
另请参阅
相关话题

非标
此特征是非标准的，且不在标准轨道中。不要在面向 Web 的生产站点中使用它：它不适用于每个用户。实现之间可能存在大的不兼容性，且行为将来可能改变。

LocalFileSystem 接口在文件系统 API gives you access to a sandboxed file system. The methods are implemented by window and worker 对象。

基本概念

This section includes a few key concepts for the methods.

Creating new storage

You request access to a sandboxed file system by calling window.requestFileSystem(). The argument of a successful callback is the FileSystem object, which has two properties: the name and root of the file system.

You can call the method more than once if you want to create two file systems: one that's temporary and one that's persistent. (To learn more about the storage types, see the 基本概念 article.) In most cases, you need to create only one file system, but in a few cases, it might be useful to create a second one. For example, if you were to create a mail app, you might create a temporary storage for caching assets (like images and attachments) to speed up performance, while creating persistent storage for unique data—such as drafts of emails that were composed while offline—that should not be lost before they are backed up into the cloud.

Using persistent storage

requestFileSystem() method lets you ask for PERSISTENT or TEMPORARY storage . Persistent storage is storage that stays in the browser unless the app or the user removes it, but the user must grant you permission before you can use it. In contrast, temporary storage is automatically granted without any user permission, but it can be expunged by the browser at any time.

要使用 PERSISTENT storage with the File System API, Chrome exposes a requestQuota API. So to request storage, you need to do something like the following:

var requestedBytes = 1024*1024*10; // 10MB
navigator.webkitPersistentStorage.requestQuota (
    requestedBytes, function(grantedBytes) {
        window.requestFileSystem(PERSISTENT, grantedBytes, onInitFs, errorHandler);
    }, function(e) { console.log('Error', e); }
);

Your user must grant your app permission to store data locally before your app can use persistent storage. Once your user grants it, you don't need to call requestQuota() again. Subsequent calls are a noop.

Another API, the Quota Management API, lets you query an origin's current quota usage and allocation using window.webkitPersistentStorage.queryUsageAndQuota() . To learn more, see this StackOverflow Answer . (An older version of the API is described at Managing HTML5 Offline Storage )。

Working within a single origin

The file system is sandboxed to a single origin. This means that your app cannot read, or write the files of another app's files. Your app cannot access files in an arbitrary folder (such as, My Pictures, My Documents) on the user's hard drive either. For more information about restrictions, see the 基本概念 article.

范例

The following is a code snippet that shows how you can request a file system storage.

//Taking care of the browser-specific prefix
window.requestFileSystem  = window.requestFileSystem || window.webkitRequestFileSystem;
// The first parameter defines the type of storage: persistent or temporary
// Next, set the size of space needed (in bytes)
// initFs is the success callback
// And the last one is the error callback
// for denial of access and other errors.
window.requestFileSystem(window.PERSISTENT, 1024*1024,onInitFs,errorHandler);

方法概述


										void
										
											requestFileSystem
										
										(in unsigned short
										
											type
										
										, in unsigned long long
										
											size
										
										, in FileSystemCallback
										
											successCallback
										
										, in optional ErrorCallback
										
											errorCallback
										
										);


										void
										
											resolveLocalFileSystemURL
										
										(in DOMString
										
											url
										
										, in EntryCallback
										
											successCallback
										
										, in optional ErrorCallback
										
											errorCallback
										
										);

常量

常量	值	描述
`TEMPORARY`	`0`	Transient storage that can be be removed by the browser at its discretion.
`PERSISTENT`	`1`	Storage that stays in the browser unless the user or the app expunges it. The user must grant permission before the app can use this type of storage.

方法

requestFileSystem()

Requests a file system where data should be stored. You access a sandboxed file system by requesting a LocalFileSystem object using this global method, window.requestFileSystem() .

void requestFileSystem(
  in unsigned short type,
  in unsigned long long size,
  in FileSystemCallback successCallback,
  in ErrorCallback errorCallback
);

参数

type

The storage type of the file system. The values can be either


								
									TEMPORARY


								
									PERSISTENT

size

The storage space—in bytes—that you need for your app.

successCallback

The success callback that is called when the browser provides a file system. Its argument is the


								
									FileSystem

object with two properties:

name - the unique name assigned by the browser to the file system.
root - the read-only DirectoryEntry object representing the root of the file system.

opt_errorCallback

The error callback that is called when errors happen or when the request to obtain the file system is denied. Its argument is the


								FileError

对象。

void

异常

This method can raise an FileError 通过以下代码：

异常	描述
`SECURITY_ERROR`	The application does not have permission to access the file system interface. For example, you cannot run from `file://` . For more details, see the article on basic concepts .

resolveLocalFileSystemURL()

Lets you look up the entry for a file or directory with a local URL.

void resolveLocalFileSystemURL(
  in DOMString url,
  in EntryCallback successCallback,
  in optional ErrorCallback errorCallback
);

参数

url
successCallback
errorCallback

void

异常

This method can raise an FileError 通过以下代码：

异常	描述
`ENCODING_ERR`	The syntax of the URL was invalid.
`NOT_FOUND_ERR`	The URL was structurally correct, but refers to a resource that does not exist.
`SECURITY_ERR`	The application does not have permission to access the file system interface.

浏览器兼容性

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.

No compatibility data found. Please contribute data for "api.LocalFileSystem" (depth: 1) to the MDN 兼容性数据存储库 .

另请参阅

规范： File API: Directories and System Specification WD

参考：文件系统 API

介绍： Basic Concepts About the File System API

元数据

最后修改： 2019 年 3 月 23 日

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