Why does window.open(…).onunload = function () { … } not work as I expect?

Question

I want to be able to tell when a window that I open is closed by the user. This is the code of my attempt at monitoring this:

  
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Answer 1

Try adding after the window loads

document.getElementById('openWindow').onclick = function () {
    var windowref = window.open('tests2.html');
    windowref.window.onload = function(){  //wait til load to add onunload event
        windowref.window.onunload =  function () {
            window.alert('hola!');
        };
    }
};

JSBin Example