Detect user status client side

[Exeter]

Is there a recommended way for detecting the user status client-side in Javascript?

I want to make slight changes to the UI depending on the user being logged in or not.

I understand that this is not secure by itself. I have proper server side validation. Page size and caching work out better if I do it this way.

Ideas:
The session cookies are secure and unreachable from JS.
I could add a field to each page from php, but that would be a custom job.

Thanks