Domain Level Cookies

Web sites often have a www. sub-domain that points to the same content as the main domain. With session cookies our visitor has either accessed our site with the www. or they have accessed it without and so the fact that a cookie created for www.example.com is not accessible from example.com isn't going to matter. With first-party cookies, a visitor may very easily access our site the first time as www.example.com and the second time as example.com and so we want to create a cookie that will be accessible from both.

Creating a Domain Level Cookie

To make a cookie accessible from the entire domain including any sub-domains we just add a domain parameter when setting the cookie as demonstrated in this JavaScript example. You should, of course, substitute your own domain name for example.com (as example.com is a domain name specifically reserved for use in examples where it represents whatever domain name you are really using.)

writeCookie = function(cname, cvalue, days) {
var dt, expires;
dt = new Date();
dt.setTime(dt.getTime()+(days*24*60*60*1000));
expires = "; expires="+dt.toGMTString();
document.cookie = cname+"="+cvalue+expires+'; domain=example.com';
}