Creating a JavaScript cookie on a domain and reading it across sub domains

Question

Below is a JavaScript cookie that is written on the user's computer for 12 months.

After we set the cookie on our main domain such as example.com, should the user visit a subdomain like test.example.com, we need to continue to identify the activity of the user across our "test" subdomain.

But with the current code, as soon as they leave www.example.com and visit test.example.com, they are no longer flagged as "HelloWorld".

Would anyone be able to help with my code to allow the cookie to be read across subdomains?

<script type="text/javascript"> var cookieName = 'HelloWorld'; var cookieValue = 'HelloWorld'; var myDate = new Date(); myDate.setMonth(myDate.getMonth() + 12); document.cookie = cookieName +"=" + cookieValue + ";expires=" + myDate; </script>

aroth · Accepted Answer · 2011-04-15 01:17:40Z

258

Just set the domain and path attributes on your cookie, like:

<script type="text/javascript"> var cookieName = 'HelloWorld'; var cookieValue = 'HelloWorld'; var myDate = new Date(); myDate.setMonth(myDate.getMonth() + 12); document.cookie = cookieName +"=" + cookieValue + ";expires=" + myDate + ";domain=.example.com;path=/"; </script>

answered Apr 15, 2011 at 1:17

aroth

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6 Comments

Idrizi.A Over a year ago

I'm trying to do this in localhost and I cannot change path

aroth Over a year ago

@Enve - Browsers treat localhost cookies a bit differently than other cookies. Or rather, they treat all cookies in a way that makes working with localhost difficult. For instance, see stackoverflow.com/questions/1134290/…. I suggest editing your hosts file and aliasing something like myserver.local to 127.0.0.1. Then you can use that to access your local server (and when setting cookies), and hopefully everything should work.

Dzeimsas Zvirblis Over a year ago

All cookie values you create & retrieve must be string values. Strings can contain characters that can upset the local storage when trying to retrieve them. One thing I would suggest is using the global encodeURI() & decodeURI() methods for the cookie name & value to handle any conversion that would need to take place. i.e. document.cookie = encodeURI(cookieName) +"=" + encodeURI(cookieValue).

CAK2 Over a year ago

If your server-side code is written in C#, Rick Strahl provides a method for getting the base domain, e.g. example.com, from the domain at weblog.west-wind.com/posts/2012/Apr/24/…

geoidesic Over a year ago

This doesn't seem to work for me. If I do this, followed by console.log(document.cookes); gives me a null return. Also nothing showing in browser storage.

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Timothy S. Van Haren · Accepted Answer · 2012-07-02 20:43:21Z

You want:

document.cookie = cookieName +"=" + cookieValue + ";domain=.example.com;path=/;expires=" + myDate;

As per the RFC 2109, to have a cookie available to all subdomains, you must put a . in front of your domain.

Setting the path=/ will have the cookie be available within the entire specified domain(aka .example.com).

FWIW - I think you need to remove the "path=expires=" piece and set it to "expires=".
As per the newer RFC 6265 it's no longer necessary to include the . in front of the domain.

ic3b3rg · Accepted Answer · 2018-12-18 17:57:38Z

Here is a working example :

document.cookie = "testCookie=cookieval; domain=." + location.hostname.split('.').reverse()[1] + "." + location.hostname.split('.').reverse()[0] + "; path=/"

This is a generic solution that takes the root domain from the location object and sets the cookie. The reversing is because you don't know how many subdomains you have if any.

This will not work if there is second level hierarchy of domain extension e.g. .co.in

Junior Tour · Accepted Answer · 2024-06-06 14:59:12Z

2

For Browser Extensions, You can also use the Cookies API and do:

browser.cookies.set({ url: 'example.com', name: 'HelloWorld', value: 'HelloWorld', expirationDate: myDate }

MDN Set() Method Documentation

edited Jun 6, 2024 at 14:59

Junior Tour

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answered Oct 28, 2016 at 5:11

rebagliatte

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1 Comment

Graeme Chapman Over a year ago

This solution only applies to browser extensions, not to javascript running in the context of a page.

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