window.addEventListener('beforeunload', function (e) {
    // Check if the user has unsaved changes
    if (unsavedChangesExist()) {
        // Display a confirmation message
        var confirmationMessage = 'You have unsaved changes. Are you sure you want to leave?';
        e.returnValue = confirmationMessage; // Standard for most browsers
        return confirmationMessage; // For some older browsers
    }
});