How the check if user closes the window/browser/shuts off computer?

I know there is a way to check if the user leaves your webpage, but what I really need is a way to check if they are still there. I'm not quite sure how t开发者_Go百科o go about doing this.

Any help is appreciated.

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You can write a call to a PHP script on regular intervals in JS letting the server know the user is still on.

This question/answers might help jquery , Ajax or PHP : Run Script at a specific time or perform action in the background