Use localStorage across subdomains

Question

I'm replacing cookies with localStorage on browsers that can support it (anyone but IE). The problem is site.example and www.site.example store their own separate localStorage objects. I believe www is considered a subdomain (a stupid decision if you ask me). If a user was originally on site.example and decides to type in www.site.example on her next visit, all her personal data will be inaccessible. How do I get all my "subdomains" to share the same localStorage as the main domain?

Answer 1

This is how I use it across domains...

• Use an iframe from your parent domain - say parent.example
• Then on each child.example domain, just do a postMessage to your parent.example iframe
• All you need to do is setup a protocol of how to interpret your postMessage messages to talk to the parent.example iframe.