如何实现浏览器当前标签是否打开或切换

<div id="number" style="display:flex;justify-content:center;align-items:center;font-size:20px;position:fixed;top:0;left:0;right:0;bottom:width:400px;height:100%;background-color:#fff;">
</div>

//网页当前状态判断
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";
}

var count = 0;
function total() {
if( document[state] == 'hidden') {
return;
}
document.querySelector("#number").innerHTML = count;
document.title = count;
count++;
}
window.setInterval(total,500);
// 添加监听器，在title里显示状态变化
document.addEventListener(visibilityChange, function() {

// document.title = document[state];
}, false);
//初始化页面状态
// document.title = document[state];

支持浏览器：