How to confirm closing a tab?

Question

JavaScript

How can I make a close confirmation window appear when I close a tab?

I saw this solution.

window.onunload = function()
{
     return confirm('Вы хотите покинуть сайт?')
}

And such

window.onbeforeunload = function(){ return 'Текст сообщения'; }

But it didn't work for me in Chrome. Probably no longer relevant code for current browsers.

The task is to show the visitor a window before closing the tab with a promotional discount code for the product.