formatNumber = n => {
  n = n.toString()
  return n[1] ? n : '0' + n
}
// 時間格式化
formatTime = date => {
  const year = date.getFullYear()
  const month = date.getMonth() + 1
  const day = date.getDate()
  const hour = date.getHours()
  const minute = date.getMinutes()
  const second = date.getSeconds()

  return [year, month, day].map(formatNumber).join('-') + ' ' + [hour, minute, second].map(formatNumber).join(':')
}
 

使用：

formatTime(new Date())