windows_onbeforeunload

<body onbeforeunload="return myFunction()">

<script>
function myFunction() {
    return "Write something clever here...";
}
</script>


<script>
window.onbeforeunload = function (e) {
    var e = e || window.event;

    // For IE and Firefox prior to version 4
    if (e) {
        console.log(1);
        e.returnValue = 'Any string';
    }

    // For Safari
    return 'Any string';
};
</script>