/**
 * Beforeunload guard — prompts the user before navigating away from unsaved changes.
 *
 * Attach to any form with a data-beforeunload-guard attribute.
 * No effect when JavaScript is unavailable (form posts normally).
 */
(function () {
    var forms = document.querySelectorAll('form[data-beforeunload-guard]');
    if (!forms.length) return;

    var dirty = false;

    for (var i = 0; i < forms.length; i++) {
        var form = forms[i];
        form.addEventListener('input', function () { dirty = true; });
        form.addEventListener('change', function () { dirty = true; });
        form.addEventListener('submit', function () { dirty = false; });
    }

    window.addEventListener('beforeunload', function (e) {
        if (dirty) {
            e.preventDefault();
        }
    });
})();