使用js倒计时还有几天及计时过了几天

公司主营业务是体育赛事为主的；尤其是足球赛事。现正值2016法国欧洲杯；之前忙于做欧洲杯专题没时间总结。现分享一个工作中需求带来的经历。

需求是：从现在开始倒计时欧洲杯还有多久开赛；当开赛之后开始计算已经开赛了几天及计算当前是小组赛还是1/8决赛,1/4决赛,半决赛,决赛。

废话不多说，直接上代码:

 var cdInterval, dateInterval;
    //此方法为倒计时欧洲杯开赛时间，原理是用开赛时间的毫秒数减去当前毫秒数然后根据每天，小时，分，秒的毫秒数向下取整
 function countDown(){
     var agent = navigator.userAgent, startTime;
     if(agent.indexOf('Trident') > -1 || agent.indexOf('Edge') > -1) { // ie,因为IE不支持new Date('xxx')创建Date对象的时候传入的时间参数，所以这里使用
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　//setUTCFullYear和setUTCHours，再getTime()等到当前毫秒数
         var euroDate = new Date();
         euroDate.setUTCFullYear('2016','05','10');//月份是从0-11的
         euroDate.setUTCHours('4','0','0','0');
         startTime = euroDate;
     } else {
         startTime = new Date("2016 06 10 12:00:00");
     }
     var nowTime = new Date(), distanceTime
         ,startServer = startTime.getTime(), nowServer = nowTime.getTime();
     distanceTime = startServer - nowServer;

     // 一天的豪秒数86400000  一个小时的毫秒数3600000  一分钟的毫秒数 60000   一秒钟的毫秒数 1000
     var d_date, d_hour, d_min,d_second;
     if(distanceTime > 0) {
         d_date = Math.floor(distanceTime/86400000); //计算还有几天
         distanceTime -= d_date*86400000;  //减去天数毫秒数计算下面的 小时数，分钟数，秒数
         d_hour = Math.floor(distanceTime/3600000);//计算小时
         distanceTime -= d_hour*3600000;//减去当前小时的毫秒数
         d_min = Math.floor(distanceTime/60000);//计算分
         distanceTime -= d_min*60000;//减去当前分的毫秒数
         d_second = Math.floor(distanceTime/1000);//计算秒
         distanceTime -= d_second*1000;//减去当前秒的毫秒数
         if(d_date < 10) {
             d_date = '0' + d_date;
         }
         if(d_hour < 10) {
             d_hour = '0' + d_hour;
         }
         if(d_min < 10) {
             d_min = '0' + d_min;
         }
         if(d_second < 10) {
             d_second = '0' + d_second;
         }
         document.getElementsByClassName('icon-time')[0].innerHTML = d_date;         document.getElementsByClassName('icon-time')[1].innerHTML = d_hour;         document.getELementsByClassName('icon-time')[2].innerHTML = d_min;         document.getElementsByClassName('icon-time')[3].innerHTML = d_second;     } else {
         clearInterval(cdInterval);
         clearInterval(dateInterval);
         $('.icon-time:not(:first)').remove();

         $('div.time span').each(function(index, item) {
             if(index !== 0 && index !== 1) {
                 $(this).remove();
             }
         });
         backwardDays()
         dateInterval = setInterval(backwardDays, 10000);
     }
 }
 //天数，原理为用当前毫秒数减去开赛时候的毫秒数计算出已经开赛了几天
 function backwardDays(){
     var dataAgent = navigator.userAgent;
     var groupGameStart = 0,groupGameEnd = 0,eighthGameStart = 0,eighthGameEnd = 0,fourGameStart = 0,fourGameEnd = 0,halfGameStart = 0,　　　　　　　　　　　　halfGameEnd = 0,
     finalGame = 0,endGame = 0;
     var dist_day = '', day = '',now_day = '';
　　　　　　//计算赛事时间
     if(dataAgent.indexOf('Trident') > -1 || dataAgent.indexOf('Edge') > -1) { //同上ie不支持new Date('xx')带参数
         var groupDayStart = new Date();
         var groupDayEnd = groupDayStart,
         eighthDayStart = groupDayStart, eighthDayEnd = groupDayStart,
         fourDayStart = groupDayStart,fourDayEnd = groupDayStart,
         halfDayStart = groupDayStart,halfDayEnd = groupDayStart,
         finalDayStart = groupDayStart,finalDayEnd = groupDayStart;
         //小组赛
         groupDayStart.setUTCFullYear('2016','05','10'); groupDayStart.setUTCHours('4','0','0','0');
         groupGameStart = groupDayStart.getTime();
         groupDayEnd.setUTCFullYear('2016','05','24');groupDayEnd.setUTCHours('4','0','0','0');
         groupGameEnd = groupDayEnd.getTime();
         //1/8决赛
         eighthDayStart.setUTCFullYear('2016','05','25'); eighthDayStart.setUTCHours('4','0','0','0');
         eighthGameStart = eighthDayStart.getTime();
         eighthDayEnd.setUTCFullYear('2016','05','28');eighthDayEnd.setUTCHours('4','0','0','0');
         eighthGameEnd = eighthDayEnd.getTime();
         //1/4决赛
         fourDayStart.setUTCFullYear('2016','06','01'); fourDayStart.setUTCHours('4','0','0','0');
         fourGameStart = fourDayStart.getTime();
         fourDayEnd.setUTCFullYear('2016','06','04');fourDayEnd.setUTCHours('4','0','0','0');
         fourGameEnd = fourDayEnd.getTime();
         //半决赛
         halfDayStart.setUTCFullYear('2016','06','07'); halfDayStart.setUTCHours('4','0','0','0');
         halfGameStart = halfDayStart.getTime();
         halfDayEnd.setUTCFullYear('2016','06','08');halfDayEnd.setUTCHours('4','0','0','0');
         halfGameEnd = halfDayEnd.getTime();
         //决赛
         finalDayStart.setUTCFullYear('2016','06','11'); finalDayStart.setUTCHours('4','0','0','0');
         finalGame = finalDayStart.getTime();
         finalDayEnd.setUTCFullYear('2016','06','11');finalDayEnd.setUTCHours('15','59','0','0');
         endGame = finalDayEnd.getTime();

     } else {
         groupGameStart = new Date("2016 06 10 12:00").getTime();
         groupGameEnd = new Date("2016 06 24 12:00").getTime(),//小组赛结束
             eighthGameStart = new Date("2016 06 25 12:00").getTime(), // 1/8决赛开始
             eighthGameEnd = new Date("2016 06 28 12:00").getTime(), // 1/8决赛结束
             fourGameStart = new Date("2016 07 01 12:00").getTime(), // 1/4决赛开始
             fourGameEnd = new Date("2016 07 04 12:00").getTime(), // 1/4决赛结束
             halfGameStart = new Date("2016 07 07 12:00").getTime(), //半决赛开始
             halfGameEnd = new Date("2016 07 08 12:00").getTime(), //半决赛结束
             finalGame = new Date("2016 07 11 12:00").getTime(), // 决赛
             endGame = new Date("2016 07 11 23:59").getTime(); // 欧洲杯结束
     }

     var currentTime = new Date().getTime();//当前时间
     //第几天
     now_day = (currentTime - groupGameStart)/86400000;
     dist_day = Math.floor((currentTime - groupGameStart)/86400000);
     if(now_day > dist_day) {//如果计算出的当前天数大于向下取整的天数，则要加1
         day = dist_day + 1;
     } else {
         day = dist_day
     }

     if(day === 0) {//day等于0的时候表示已经开赛，所以计算为第一天
         day = 1;
     }
     if(day < 10) {
         day = '0' + day;
     }
     $('.icon-time:eq(0)').text(day);
        //根据时间范围算出赛事范围
     if(currentTime >= groupGameStart && currentTime <= groupGameEnd) {//小组赛
         $("em.gameType").text($('#xzs').val());
     } else if(currentTime >= eighthGameStart && currentTime <= eighthGameEnd) {// 1/8 决赛
         $("em.gameType").text("1/8"+$('#jsi').val());
     } else if(currentTime >= fourGameStart && currentTime <= fourGameEnd) {// 1/4决赛
         $("em.gameType").text("1/4"+$('#jsi').val());
     } else if(currentTime >= halfGameStart && currentTime <= halfGameEnd) {// 半决赛
         $("em.gameType").text($('#bjs').val());
     } else if(currentTime >= finalGame && currentTime <= endGame) { //决赛
         $("em.gameType").text($('#jsi').val());
     } else {
         $("em.gameType").text("");
     }

     if(currentTime >= endGame) {
         clearInterval(dateInterval);
     }
 }
 $(function(){
     clearInterval(cdInterval);
     cdInterval = setInterval(countDown,1000);
 });