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setCookie

The

setCookie()

function systematically builds up a cookie string based on the arguments passed in.

Only the first two arguments are required, so the function checks to make sure that each argument exists

before it’s added to the cookie string. The third argument is expected to be a

Date

object so the

toGMTString()

method can be called. At the end of the function, the

document.cookie

is set with

the cookie string. This function is used as follows:

setCookie(“name”, “Nicholas”);

setCookie(“book”, “Professional JavaScript”, new Date(Date.parse(“Jan 1, 2006”)));

setCookie(“message”, “Hello World! “, new Date(Date.parse(“Jan 1, 2006”)),

“/books”, “http://www.wrox.com”, true);

The next function,

getCookie()

, retrieves the value of a cookie when the name is passed in:

function getCookie(sName) {

var sRE = “(?:; )?” + sName + “=([^;]*);?”;

var oRE = new RegExp(sRE);

if (oRE.test(document.cookie)) {

return decodeURIComponent(RegExp[“$1”]);

} else {

return null;

}

This function uses a regular expression built out of the name of the cookie. Regular expressions are the

easiest way to extract a particular value from

document.cookie

because of the cookie string format. If

there’s only one cookie, then the string is a simple name and value pair, and the value is all the characters

after the equal sign up to the end of the string. If more cookies follow, they are separated by semicolons.

This means that the value for any cookie (other than the last one) comprises all characters after the equal

sign but before the next semicolon. The regular expression makes it easy to take all this into account, set-

ting up a capturing group to retrieve the cookie value. You can then get the values of cookies like so:

var sName = getCookie(“name”);

var sBook = getCookie(“book”);

var sMessage = getCookie(“message”);

The last function is

deleteCookie()

, which immediately removes a cookie from the system. As men-

tioned previously, setting its expiration time to a past date can accomplish this. In order have this work,

however, the path and domain information must be the same as when you created the cookie, so these

must also be arguments:

function deleteCookie(sName, sPath, sDomain) {

setCookie(sName, “”, new Date(0), sPath, sDomain);

}

Because

setCookie()

sets all the same information as

deleteCookie()

, it makes sense just to use it

and pass in an expiration date that already occurred (in this case, January 1, 1970).

Using these functions, it’s easy to manipulate cookies using JavaScript. Even if the server creates cookies,

JavaScript can still read them, which is where the real power lies.

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