Authentication timeout while making AJAX call?

Hi,
I tried to take advantage of jQuery AJAX call to enhance user experience but I am facing a tricky problem.
When the user does nothing for a period of time, e.g. 30 minutes to reach authentication timeout, making AJAX call becomes the problem. The server side will return login page and display in my target div section. The simplest solution I can think of is to inject a dummy tag in login page, and when detecting such dummy tag then use javascript to redirect to login page. But this means that I have to do that every time I make AJAX call.
Is there any more decent way to do that?


Regards,
Charlie

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