Chapter 3. Getting Started

Opening a Filesystem

A web application obtains access to the HTML5 Filesystem by requesting a LocalFileSystem object using a global method, window.requestFileSystem():

window.requestFileSystem(type, size, successCallback, opt_errorCallback)


This method is currently vendor prefixed as window.webkitRequestFileSystem.

Its parameters are described below:


Whether the storage should be persistent. Possible values are TEMPORARY or PERSISTENT. Data stored using TEMPORARY can be removed at the browser’s discretion (for example if more space is needed). PERSISTENT storage cannot cleared unless explicitly authorized by the user or the application.


An indicator of how much storage space, in bytes, the application expects to need.


A callback function that is called when the user agent successfully provides a filesystem. Its argument is a FileSystem object.


An optional callback function which is called when an error occurs, or the request for a filesystem is denied. Its argument is a FileError object.

Calling window.requestFileSystem() for the first time creates a new sandboxed storage space for the app and origin that requested it. A filesystem is restricted to a single application and cannot access another application’s stored data. This also means that an application cannot read/write files to an arbitrary folder on the user’s hard drive (such as My Pictures or My Documents). Each filesystem is isolated.

Example 3-1. Requesting ...

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