javascript

Chapter 19: Client - Side Storage
The accessibility restrictions on IE user data are similar to the restrictions on cookies. In order to access a
data store, the page on which the script is running must be from the same domain, on the same directory
path, and using the same protocol as the script that saved data to the store. Unlike with cookies, you
cannot change accessibility restrictions on user data to a wider range of consumers. Also unlike cookies,
user data persists across sessions by default and doesn ’ t expire; data needs to be specifically removed
using removeAttribute() in order to free up space.
As with cookies, IE user data is not secure and should not be used to store sensitive
information.
DOM Storage
DOM Storage was first described in the Web Applications 1.0 specification of the Web Hypertext Application
Technical Working Group (WHAT - WG). The initial work from this specification eventually became part of
HTML 5 (see Chapter 21 ), but prior to that point, numerous browsers had implemented DOM Storage. Its
intent is to overcome some of the limitations imposed by cookies when data is needed strictly on the client
side, with no need to continuously send data back to the server. The two primary goals of DOM Storage are:
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To provide a way to store session data outside of cookies
To provide a mechanism for storing large amounts of data that persists across sessions
The original DOM Storage specification included definitions for two objects: sessionStorage and
globalStorage . The latter was replaced in HTML 5 by localStorage . Each of these objects has been
implemented by at least one browser and is a global variable, available as a property of window .
DOM Storage has been partially implemented by Firefox 2 and later, and fully
implemented in IE 8 and Safari 3.1. Chrome is expected to implement it before
reaching version 1.0, and Firefox is expected to complete its implementation in
version 3.1.
The Storage Type
The Storage type is designed to hold name - value pairs up to a maximum size (determined by the
browser). An instance of Storage acts like any other object and has the following additional methods:
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clear() — Removes all values; not implemented in Firefox
getItem( name ) — Retrieves the value for the given name
key( index ) — Retrieves the name of the value in the given numeric position
removeItem( name ) — Removes the name - value pair identified by name
setItem( name , value ) — Sets the value for the given name
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