判断当前窗口是否活动窗口

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// 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]