What does this code mean?

this paragraph is the countdown code, what does he mean?
function checkTime (i)

{
    if(i<10)
    {
        i="0"+i;
    }
    return i;
}
var time = setInterval("showTime()",500);
function showTime()
{
  var timedate= new Date("2018/12/01,10:13:55");                  
var now = new Date();                                         
var date = parseInt(timedate.getTime() - now.getTime())/1000; 
  if(date <= 0)
  {
      document.getElementById("txtshow").innerHTML="";
      clearInterval(time);
  }
var day = parseInt(date/60/60/24);     
    var hour = parseInt(date/60/60%24);
    var minute = parseInt(date/60%60);
    var second = parseInt(date%60);
    hour = checkTime(hour);
    minute = checkTime(minute);
    second = checkTime(second);
    var leftTime = day+""+hour+""+minute+""+second+"";
    document.getElementById("timeShow").innerHTML = leftTime;
    time;        













Mar.03,2021

countdown function.


//100  10:01 
function checkTime(i){
    if(i<10)
    {
        i="0"+i;
    }
    return i;
}

function showTime()
{
  var timedate= new Date("2018/12/01,10:13:55");                  
var now = new Date();                                         
var date = parseInt(timedate.getTime() - now.getTime())/1000; //

    //0
  if(date <= 0)
  {
      document.getElementById("txtshow").innerHTML="";
      clearInterval(time);
  }
    //dom
var day = parseInt(date/60/60/24);     
    var hour = parseInt(date/60/60%24);
    var minute = parseInt(date/60%60);
    var second = parseInt(date%60);
    hour = checkTime(hour);
    minute = checkTime(minute);
    second = checkTime(second);
    var leftTime = day+""+hour+""+minute+""+second+"";
    document.getElementById('timeShow').innerHTML = leftTime;
    time;  
    
   }      

//500dom
var time = setInterval('showTime()',500);

Menu