Chapter 19. Cookies and Client-Side Persistence
The Document object has a property named
cookie that was not discussed in Chapter 15. On the surface, this property appears to
be a simple string value; however, the
cookie property is much more than this: it
disk and to retrieve data that was previously stored in this way.
Client-side persistence is an easy way to give web applications a
memory: a web site can store user preferences so that they can be used
again when the user revisits the page, for example.
Cookies are also used for server-side scripting and are a standard
extension to the HTTP protocol. All modern web browsers support them and
allow them to be scripted with the
Document.cookie property. There are other
client-side persistence mechanisms that are more powerful but less
standard than cookies, and I discuss them briefly at the end of this
An Overview of Cookies
A cookie is a small amount of named data stored by the web browser and associated with a particular web page or web site.[*] Cookies serve to give the web browser a memory so that scripts and server-side programs can use data that was input on one page on another page, or so the browser can recall user preferences or other state variables when the user leaves a page and then returns. Cookies were originally designed for server-side programming, and at the lowest level, they are implemented as an extension to the HTTP protocol. ...