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 LocalFileSystemSync interface of the File System API gives you access to a sandboxed file system. It is intended to be used with WebWorkers. The methods are implemented by worker objects.

About this document

This document was last updated on March 2, 2012 and follows the W3C Specifications (Working Draft) drafted on April 19, 2011.

This specification is more or less abandonned, failing to get significant traction.

Basic concepts

You can request access to a sandboxed file system by requesting LocalFileSystemSync object from within a web worker. The global methods in the window object requestFileSystemSync() and resolveLocalFileSystemSyncURL() methods are exposed to the Worker's global scope. Calling window.requestFileSystemSync() for creates new storage for your web app.

For more concepts, see the counterpart article for the asynchronous API.


//Taking care of the browser-specific prefix
window.requestFileSystemSync  = window.requestFileSystemSync || window.webkitRequestFileSystemSync;

// 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. 

var fs = requestFileSystemSync(TEMPORARY, 1024*1024 /*1MB*/);

Because you are using a synchronous API, you don't need success and error callbacks.

Method overview

FileSystemSync requestFileSystemSync (in unsigned short type, in long long size) raises FileException;
EntrySync resolveLocalFileSystemSyncURL (in DOMString url) raises FileException;


Constant Value Description

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.



Requests a file system where data should be stored. You access a sandboxed file system by requesting a LocalFileSystemSync object from within a web worker using this global method, window.requestFileSystemSync(). [ RESEARCH ]

<code>FileSystemSync</code> requestFileSystemSync(
  in unsigned short type, 
  in unsigned long long size  
The storage type of the file system. The values can be either TEMPORARY or PERSISTENT.
The storage space—in bytes—that you need for your app.
An object that represents the file system.

This method can raise an FileException with the following code:

Exception Description
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.


Allows the user to look up the Entry for a file or directory referred to by a local URL.

void resolveLocalFileSystemURL(
  in DOMString url  
The URL of a local file in the file system.
An object that represents entries in the file system.

This method can raise a FileException with the following codes:

Exception Description
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.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 13webkit Not supported Not supported Not supported Not supported
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support Not supported 0.16webkit Not supported Not supported Not supported Not supported

See also

Specification:File API: Directories and System SpecificationWD

Reference: File System API

Introduction: Basic Concepts About the File System API


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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

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