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Cookies in JavaScript

Dealing with cookies in JavaScript is a little complicated because of a notoriously poor interface. The

document

object has a property called

, which is a single string containing all cookies accessible

by the given page. The

property is also unique in that setting it to a specific value only alters the

cookies available to the page; it doesn’t actually change the value of

itself. This functionality is

part of the BOM and, as such, isn’t guided by any sort of specifications (which explains its lack of logic).

To create a cookie, you must create a string in the following format:

cookie_name=cookie_value; expires=expiration_time; path=domain_path;

domain=domain_name; secure

Only the first part of the string, specifying the name and value, is mandatory to set a cookie; all other

parts are optional. This string is then set to the

document.cookie

property to create the cookie. For

example, to set a simple cookie, use the following:

document.cookie = “name=Nicholas”;

document.cookie = “book=” + encodeURIComponent(“Professional JavaScript”);

Reading the value of

document.cookie

gives access to these cookies, along with all others accessible

from the given page. If you display the value of

document.cookie

after running the two lines of the

previous code, it equals

“name=Nicholas; book=Professional%20JavaScript”

. Even if other

cookie attributes are specified, such as an expiration time,

document.cookie

only returns the name

and value of each cookie with a semicolon separating the cookies.

Because creating and reading cookies requires remembering this format, most developers use functions

to handle the details. The function to create a cookie is the easiest:

function setCookie(sName, sValue, oExpires, sPath, sDomain, bSecure) {

var sCookie = sName + “=” + encodeURIComponent(sValue);

if (oExpires) {

sCookie += “; expires=” + oExpires.toGMTString();

}

if (sPath) {

sCookie += “; path=” + sPath;

}

if (sDomain) {

sCookie += “; domain=” + sDomain;

}

if (bSecure) {

sCookie += “; secure”;

}

document.cookie = sCookie;

}

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Client-Server Communication

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