I know this is a very simple question but even of being a simple question I yet don't find answers to it:

How do I handle if a user confirms to close the page and execute an action in that moment?

Here's the code:

window.addEventListener('beforeunload', function (e) {
    e.preventDefault();
    e.returnValue = '';
    // handle if user confirms to close window
    // if so then call a function (ex, do something)
});

HOW DO I ACHIEVE THIS?

IMPORTANT:

I want to make an API call to alter server side data when the user closes the window, what is more suitable to achieve such goal based on the base question?