判断当前窗口是否活动窗口

		// 各种浏览器兼容
		var hidden, state, visibilityChange;
		if (typeof document.hidden !== "undefined") {
		  hidden = "hidden";
		  visibilityChange = "visibilitychange";
		  state = "visibilityState";
		} else if (typeof document.mozHidden !== "undefined") {
		  hidden = "mozHidden";
		  visibilityChange = "mozvisibilitychange";
		  state = "mozVisibilityState";
		} else if (typeof document.msHidden !== "undefined") {
		  hidden = "msHidden";
		  visibilityChange = "msvisibilitychange";
		  state = "msVisibilityState";
		} else if (typeof document.webkitHidden !== "undefined") {
		  hidden = "webkitHidden";
		  visibilityChange = "webkitvisibilitychange";
		  state = "webkitVisibilityState";
		}

		// 添加监听器，在title里显示状态变化
		document.addEventListener(visibilityChange, function() {
		  document.title = document[state];
		}, false);

		// 初始化
		document.title = document[state]