JS 日期時間格式的字符串 轉 yyyy-MM-dd格式的字符串

formatDate(dateString) {
  var d = new Date(dateString),
    month = '' + (d.getMonth() + 1),
    day = '' + d.getDate(),
    year = d.getFullYear()
  
  if (month.length < 2) month = '0' + month
  if (day.length < 2) day = '0' + day
  return [year, month, day].join('-')
},