Check if user closed the page in PHP?

[JessieS]

I made a chat using PHP and JavaScript chat and there is a disconnect button which removes user from the chat removing him from user list first. But if the user closes browser then he will remain in the user list. How do I check if he left?This must be done without putting any handles on page closing in JS because if user kills the browser then he will remain in chat.By the way , JS script always sends a request to the PHP page which constantly checks for new messages in a loop and when there are some, the script prints them out and exits. Then it repeats all over again.EDIT : How do I make a heartbeat thing in PHP? If a user closes the page the script execution will be terminated therefore we won't be able to check if the user is still connected in the same script.