<!--离开页面改变title-->
var time;
var norm_title = document.title;
document.addEventListener('visibilitychange', function () {
	if (document.visibilityState == 'hidden') {
		clearTimeout(time);
		document.title = '离开时的内容';
	} else {
		document.title = '回来时的内容';
		time = setTimeout(function () {
			document.title = normar_title;
		}, 3000);
	}
});