var titleTime, oldTitle = document.title;

document.addEventListener("visibilitychange", function() {

  if (document.hidden) {

      document.title = "咦，去哪儿啊？";

      clearTimeout(titleTime);

      document.getElementById('shortcut').href = "images/fail.ico";

  }

  else{

      document.title = "欢迎回来！" + oldTitle;

      document.getElementById('shortcut').href = "images/favicon.ico";

      titleTime = setTimeout(function(){

          document.title = oldTitle;

      }, 2e3)

  }

})