function addDays(date, days,seperator='-') {  let oDate = new Date(date).valueOf();  let nDate = oDate + days * 24 * 3600 * 1000;  nDate = new Date(nDate);  let y = nDate.getFullYear().toString().padStart(2, 0);  let m = (nDate.getMonth() + 1).toString().padStart(2, 0);  let d = nDate.getDate().toString().padStart(2, 0);  return `${y}${seperator}${m}${seperator}${d}`}

 

 

addDays('2019-06-03 09:30:30',6)

　　"2019-06-09"