jsミリ秒(タイムスタンプ)と日付は互いに変換されます.

let  data =  1537444800000
//           string，     int
let dateTime = getMyDate(parseInt(data));
//   dateTime：2018-09-20 20:00:00
  //   
function getMyDate(str) {
     
    let oDate = new Date(str),
    oYear = oDate.getFullYear(),
    oMonth = oDate.getMonth()+1,
    oDay = oDate.getDate(),
    oHour = oDate.getHours(),
    oMin = oDate.getMinutes(),
    oSen = oDate.getSeconds(),
    oTime = oYear +'-'+ addZero(oMonth) +'-'+ addZero(oDay) +' '+ addZero(oHour) +':'+
addZero(oMin) +':'+addZero(oSen);
    return oTime;
}
//    
function addZero(num){
     
    if(parseInt(num) < 10){
     
        num = '0'+num;
    }
    return num;
}

let dateTime = '2018-09-20 20:00:00'
var secondsTime = new Date(dateTime).getTime();
secondsTime:  1537444800000