window.onbeforeunload - Only show warning when not submitting form

I am using window.onbeforeunload to prevent the user from navigating away after changing values on a form. This is working fine, except it also shows the warning when the user submits the form (not desired).

How can I do this without showing the warning when the form submits?

Current code:

var formHasChanged = false;

$(document).on('change', 'form.confirm-navigation-form input, form.confirm-navigation-form select, form.confirm-navigation-form textarea', function (e) {
    formHasChanged = true;
});

$(document).ready(function () {
    window.onbeforeunload = function (e) {
        if (formHasChanged) {
            var message = "You have not saved your changes.", e = e || window.event;
            if (e) {
                e.returnValue = message;
            }
            return message;
        }
    }
});