So far, you've learned how to set and read a basic
cookie.
Unfortunately,
your basic cookie will get deleted automatically
when a user
quits out of
the browser. Sometimes this is for
the best.
Since each domain, such as
webmonkey.com, is allowed
only 20 cookies on
any user's machine,
you
don't want to waste space with cookies that
aren't saved between
browser sessions.
However, if
you
do want to save cookies on
users' hard drives,
you
have to set an expiration date,
which has to be
in a special format called
GMT. For
example:
Mon, 27-Apr-1998 00:00:00 GMT
(This is the date on which Koko the gorilla had
her
AOL chat session.)
Getting the GMT right can be sort of a
pain,
especially
when it comes to figuring out the day of the date. Is it a Monday?
A
Friday? To make
things easier on you, JavaScript has a date method
called
toGMTString.
Here's an easy way to set an expiration date to
some
distant time in the future:
var the_date = new Date("December 31, 2023");
var the_cookie_date = the_date.toGMTString();
Once you establish
an
expiration date for your cookie,
you have to add this information
before
you
set the cookie. Therefore, your cookie should
look
like this:
cookie_name=blah_blah;expires=date
Basically, you're just adding expires=date to
the
cookie
string and separating the different cookie components
with
a
semicolon.
Here's how to build a cookie that will last
until the
end
of the Mayan calendar:
function setCookie()
{
// get the information
//
var the_name = prompt("What's your name?","");
var the_date = new Date("December 31, 2023");
var the_cookie_date = the_date.toGMTString();
// build and save the cookie
//
var the_cookie = "my_cookie=" + escape(the_name);
the_cookie = the_cookie + ";expires=" + the_cookie_date;
document.cookie = the_cookie;
}
At the end of all
this, the_cookie will look
something
like this:
my_cookie=thau;expires=Fri, 31-Dec-2023 00:00:00 GMT
When this cookie is
set, it will
live on the user's hard drive until
the expiration date.
The
expiration date also allows you to delete cookies you don't
want users to
have any more. If you set the expiration date of a cookie to
a time that's
already passed, the cookie will be deleted from the
cookie
file.
In addition to name and
expires,
there are two other important cookies components that
you'll need to know
about: path and domain.
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