check if changes saved before unload

I have the following javaScript

EDIT: included assignments for cahngesSaved

 var changesSaved = true;

    $(document).ready(function () {

        $(".applyChanges").click(function (e) {
            e.preventDefault();
            var id = (this).id;
            var dayofweek = document.getElementById("dayofweek" + id).value;
            var hour = document.getElementById("hour" + id).value;
            var duration = document.getElementById("duration" + id).value;
            $.ajax({
                url: '@Url.Action("ApplyChanges")',
                type: 'POST',
                data: {
                    id: id,
                    dayofweek: dayofweek,
                    hour: hour,
                    duration: duration
                },
                success: function (data) {
                    $('#Calendar').fullCalendar('refetchEvents')
                    $('#Calendar2').fullCalendar('refetchEvents')
                    changesSaved = false;
                }
            });
        });
    });

window.onbeforeunload = function () {
    if (changesSaved == true) {
        return true;
    } else {
        return ("You havent saved your changes. Are you sure you want to leave the page?")
    }
}

but the message is being prompted regardless of what changesSaved is set too.

What actually I actually get is the following:

or if changesSaved is set to false it says false instead.

Can i not do this ?

Derek 朕會功夫

<body onbeforeunload="return bye()">

function bye(){
    if(changesSaved) {
        return "You havent saved your changes."
    }
}

This is how I do it.

or in pure JavaScript:

window.onbeforeunload = function() {
    if (changesSaved) {
        return "You haven't saved your changes.";
    }
};

window.onbeforeunload = function () {
     var changesSaved = confirm("You havent saved your changes. Are you sure you want to leave the page?");
    if (changesSaved) {
        return true;
    } else {
        return false;
    }

来源：https://stackoverflow.com/questions/10873546/check-if-changes-saved-before-unload

标签

javascript

javascript-events

onbeforeunload

onunload