Jquery检查当前浏览器选项卡是否处于活动状态

Question

我需要在活动的浏览器选项卡上运行脚本。如果打开的选项卡很少，则仅在激活时运行它。如果隐藏了所有选项卡，则仅在上次访问（非关键）或任何单个选项卡时运行脚本。

我编写了代码，但是sumtimes焦点事件不会触发。

var page_id = $page_id; //unique id

// write page id in array in cookie
var pages = [];
if ($.cookies.get('pages') != null) {
    pages = $.cookies.get('pages');
}
//set active page to false
pages[page_id] = false;

//if none of opened pages are active set current page active
var count = 0;
$.each(pages, function( index, value ) {
    if (value == true) {
        count++;
    }
});
if (count == 0) {
    pages[page_id] = true;  
    $.cookies.set('pages', pages, {hoursToLive: .1});
}

// if current page is active run script
if (pages[page_id] == true) {
    run_script();
}

$(function() {
    // on page focus
    $(window).focus(function() { 
        pages = $.cookies.get('pages');
        //if empty cookies write current page in cookie
        if (jQuery.isEmptyObject(pages)) {
            pages = {};
            pages[page_id] = true;
        // non of pages are active write current page as active
        } else {
            var count = 0;
            $.each(pages, function( index, value ) {
                if (index == page_id) {
                    count++;
                    pages[index] = true;    
                } else {
                    pages[index] = false;
                }
            });
            if (count == 0) {
                pages[page_id] = true;
            }
        }
        $.cookies.set('pages', pages, {hoursToLive: .1});
    });
});

//before close page delete it's id from cookie
window.onbeforeunload = function() {
    var pages = {};
    if ($.cookies.get('pages') != null) {
        pages = $.cookies.get('pages');
    }
    delete pages[page_id];
    $.cookies.set('pages', pages, {hoursToLive: .1});
};

// if empty cookie write current page
window.setInterval(function(){
    pages = $.cookies.get('pages');
    if (jQuery.isEmptyObject(pages)) {
        pages = {};
        pages[page_id] = true;
    }
    $.cookies.set('pages', pages, {hoursToLive: .1});
}, 1000);