open a custom popup on browser window/tab close

Question

I am trying to open a custom popup on browser window/tab close.

In details if a user clicks on the browser window/tab close button a custom popup will appear with s

Answer 1

window.onbeforeunload = function (e) 
{
    e = e || window.event;

        e.returnValue = 'You want to leave ? ';


};

jsFiddle