Use javascript to determine if the user is logged into Joomla

I have a joomla page which updates regularly using AJAX. Depending on other (external) events, the user may get logged out of the site. I would like to be able to tell fro开发者_如何学Cm Javascript whether the user is (still) logged in. I am looking for some sort of Javascript function which will make a call to the server and will return true if the user is logged in or false if they are not logged in.

Thanks for any ideas.

Here's how to fire a controller function in your component using jQuery.

$.post("index.php?option=com_mycomponent", {task: "checkUserStatus", username: "chuck"},
    function(data)
    {
        //do something with your 'data' response here
    });

Just as reminder - make sure and close the mainframe at the end of your controller function, otherwise Joomla will render the whole component and flush the output to the data variable.

function checkUserStatus()
{
    //do your PHP code to check user status

    echo $response;

    global $mainframe;
    $mainframe->close();
}