Question

Possible Duplicate:
Check if user is logged in New Facebook API

ive implemented facebook login intergration within my site. everything works as should. except that, i want a script to know if someone is logged into facebook, to have the option to autologin. lemme give you a better example, go to http://bit.ly/iaUiEf when logged into facebook. it will popup this feature. is this an fb feature?

Answer 1

You can use HTTP Headers to see if a user is logged in to Facebook, via Javascript as explained by this post

<script type="text/javascript"
        src="https://www.facebook.com/imike3"
        onload="logged_in_to_facebook()"
        onerror="not_logged_in_to_facebook()"
        async="async"
></script>

See the linked post to see the whole explanation. But briefly, using a script tag.. the user’s browser is asked to fetch a certain profile page. That profile page’s permissions is setup so that only logged in users in facebook will be able to see it. Thus, return with a Status 200 and triggers the onload event. Even though the page does not contain valid Javascript, the browser will just ignore it.