var dialog = document.getElementByTagName('dialog');
dialog.showModal();
dialog.addEventListener('click',function (event) {
    var rect = dialog.getBoundingClientRect();
    var isInDialog=(rect.top <= event.clientY && event.clientY <= rect.top + rect.height
      && rect.left <= event.clientX && event.clientX <= rect.left + rect.width);
    if (!isInDialog) {
        dialog.close();
    }
});