可以获取当前日期和自定义获取某天的日期。

function getFormatDate(customDate = 0) {
  var nowDate = new Date();
  var time = 24 * 60 * 60 * 1000;
  var date = new Date(nowDate.getTime() + time * customDate) ;
  var connect = "-";
  var year = date.getFullYear();
  var month = date.getMonth() + 1;
  var day = date.getDate();
  if( month <= 9) {
    month = "0" + month;
  }
  if(day <= 9) {
    day = "0" + day;
  }
  var nowFormatDate = year + connect + month + connect + day;
  return nowFormatDate;
}

//使用
var dateFomate1 = getFormatDate() ; //当前日期
var dateFomate2 = getFormatDate(-7) ; //7天前日期
var dateFomate3 = getFormatDate(30) ; //30天后日期