[TYPO3] newloginbox - check user state logged in?

[Katharina]

Hi there,

I'm using the newloginbox extension, and I want to know if there is a 
chance to check if a FE user is logged in or not with some sort of code
(e.g. java script)?
My aim is to display a link to the login page defined in my template 
file for my typo3 website. The link is named 'login' and if the user
  is already logged in I would like to have 'log out' displayed instead.

I would ve very thankful for every hint I get to solve that problem...

Best regards,

             Katharina