What is Web Storage (DOM Storage)?

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Web Storage (also called DOM Storage or super cookies) is a technique for Web applications to store data in a web browser.

DOM Storage is standardized by the World Wide Web Consortium (W3C). Originally it was part of the HTML5 specification, but has now been spun off into a separate specification.

Currently, DOM Storage works with Internet Explorer 8, Mozilla based browsers (eg Firefox 2 +, officially since 3.5), Safari 4, Google Chrome 4, and Opera support 10:50.

Features

DOM Storage can be described as an evolution of cookies into super cookies. The technique provides much greater storage capacity (5MB per domain in Firefox, 10MB per storage area in Internet Explorer) and developing better interfaces. In some respects, however, it differs from cookies.

Client-side interface

In contrast to cookies, both server and client can access the DOM Storage fully controlled by the client. Data is not transmitted with every HTTP request to the server and a web server can not write data directly in the DOM Storage. Access is only via scripts on the page.

Storage

DOM Storage provides two different types of storage: local storage and session storage. They vary in scope and duration.

Local storage

Data that is stored locally, Local Shared Objects (LSO), is linked to a domain and remains there even after the browser is closed. All scripts on a domain, from which the data was stored, can access the data.

In Mozilla Firefox, the data is stored in the database file. The SQLite3 file can be viewed using a suitable program. There are browser add-ons that are needed for the purpose that you can delete this information from your system again, some are automated, eg with Better Privacy.

By entering about: config in the address bar, the value of dom.storage.enabled can changed to false from true, and DOM Storage objects are thus switched off.

Session specific storage

Session specific data is associated with the browser window and limited to this. Stored data will be deleted when you close the browser window.

This technique provides the ability to run multiple instances of the same application running in different windows, without that there is a mutual influence, which is not supported by cookies.

Data model

DOM Storage stores data in an associative array where the keys and values are strings.

Naming

The abbreviation DOM in DOM Storage is not in direct connection to the Document Object Model. The term DOM refers to the application interfaces that are scripts in Web applications, and does not necessarily imply the existence of an actual Document object.

Similar technologies

HTTP cookies
Local Shared Objects in Flash
Google Gears for IE , Firefox, Safari and Windows Mobile

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