SOURCE

var str = '2020/12/04 10:00:00'
var endTime = new Date(str)

var nowTime = new Date() 
function autoCount(){
   var nowTime = new Date()
   var lenTime = endTime.getTime() - nowTime.getTime()
   var h = Math.floor(lenTime/1000/60/60%24)<10?('0'+ Math.floor(lenTime/1000/60/60%24)):Math.floor(lenTime/1000/60/60%24),
       min = Math.floor(lenTime/1000/60%60)<10?('0' + Math.floor(lenTime/1000/60%60)):Math.floor(lenTime/1000/60%60),
       sec = Math.floor(lenTime/1000%60)<10? ('0' + Math.floor(lenTime/1000%60)):Math.floor(lenTime/1000%60)
    console.log(h, min, sec)
}

// setInterval(autoCount, 1000)
var year = nowTime.getFullYear()
console.log(year)
var mounth = (nowTime.getMonth() + 1) <10?('0' + (nowTime.getMonth() + 1)):(nowTime.getMonth() + 1)
console.log(mounth)
var date = nowTime.getDate() < 10? ('0' +  nowTime.getDate()) : nowTime.getDate()
console.log(date)
var hour = nowTime.getHours() < 10? ('0' +  nowTime.getHours()) : nowTime.getHours()
var min = nowTime.getMinutes() < 10? ('0' + nowTime.getMinutes()) : nowTime.getMinutes()
var sec = nowTime.getSeconds() < 10? ('0' + nowTime.getSeconds()) : nowTime.getSeconds()
console.log(year+'/'+mounth+'/'+date+' '+hour+':'+min+':'+sec)