正则表达式实现字符串每4位后自动加空格效果

<input type="text" v-model="bankCard" @keyup="bankCardKeyup">
bankCardKeyup (e) {
  let self = this
  // 如果是删除键，则不加空格，且删去字符串末端空格
  if (e.keyCode === 8) {
  self.bankCard = self.bankCard.replace(/[\s\n\t]+$/g, "")
  return
  }
  self.bankCard = self.bankCard.replace(/[^0-9|' ']/g, '')
  let value = self.bankCard.replace(/[^0-9]/g, '')
  if (value.length > 4 && value.length <= 8) {
  self.bankCard = value.slice(0, 4) + ' ' + value.slice(4, value.length)
  }
  else if (value.length > 8 && value.length <= 12) {
  self.bankCard = value.slice(0, 4) + ' ' + value.slice(4, 8) + ' ' + value.slice(8, value.length)
  }
  else if (value.length > 12 && value.length <= 16) {
  self.bankCard = value.slice(0, 4) + ' ' + value.slice(4, 8) + ' ' + value.slice(8, 12) + ' ' + value.slice(12, value.length)
  if (value.length === 16) {
   // 调用识别银行卡函数

  }
  }
  else if (value.length > 16) {
  self.bankCard = value.slice(0, 4) + ' ' + value.slice(4, 8) + ' ' + value.slice(8, 12)+ ' ' + value.slice(12, 16) + ' ' + value.slice(16, value.length)
  if (value.length === 19) {
   // 调用识别银行卡函数

  }
  else if (value.length > 19) {
   self.bankCard = value.slice(0, 4) + ' ' + value.slice(4, 8) + ' ' + value.slice(8, 12)+ ' ' + value.slice(12, 16) + ' ' + value.slice(16, 19)
  }
  }
 },

<input type="text" v-model="bankCard" @keyup="bankCardKeyup">
bankCardKeyup () {
 let self = this
 self.bankCard = self.bankCard.replace(/\s/g,'').replace(/[^\d]/g,'').replace(/(\d{4})(?=\d)/g,'$1 ')
}