js如何判断当前页面窗口在浏览器是否处于激活状态

方式1：监听事件visibilitychange

var hiddenProperty = 'hidden' in document ? 'hidden' :    
        'webkitHidden' in document ? 'webkitHidden' :    
        'mozHidden' in document ? 'mozHidden' :  null;
var visibilityChangeEvent = hiddenProperty.replace(/hidden/i, 'visibilitychange');
var onVisibilityChange = function(){
        if (!document[hiddenProperty]) {    
                alert("未激活状态！");
        }else{
                alert("激活状态！")
        }
}

document.addEventListener(visibilityChangeEvent, onVisibilityChange);
方式2：监听事件blur和focus

window.onblur = function(e){
    console.log("未激活状态！")
}
window.onfocus = function(e){
    console.log("激活状态！")
}