Unable to retrieve current Parse user

I'm logging into my Parse app through the JavaScript SDK, it appears to be storing cookies however once it progresses to the next page it always displays the current user as being null despite having logged in successfully. I've cleared the cookies and it appears to be storing the cookies after login fine. This is the code I'm using however no matter what I seem to do it just won't collect the current user. Does anyone know if there's an issue with this or if there's something extra I have to do for it to be able to recall the cookie? If it's relevant the two site are on subdomains, could this be the problem?

Parse.initialize(JSDK, API);
                var currentUser = Parse.User.current();
                var currentUsername = currentUser.get('username');
                alert(currentUsername);