如何实现vue输入电话号码自动按3-4-4分割功能

<input class="inputBox" type="phone" 
placeholder=" 请输入手机号" 
maxlength="13" v-model="phoneNum"/>

watch: {
 phoneNum (newValue, oldValue) { // 监听电话号码
 this.phoneNum = newValue.length > oldValue.length ? newValue.replace(/\s/g, '').replace(/(\d{3})(\d{0,4})(\d{0,4})/, '$1 $2 $3') : this.phoneNum.trim()
 if (this.phoneNum.length === 13) {
 // 验证/保存的手机号码，去除空格
 this.state.checkPhoneNum = this.phoneNum.replace(/\s/g, '')
 console.log('输入的电话号码是：', this.state.checkPhoneNum)
 } 
 }
 },

<template>
 <div class="form">
 <p>
 手机号：
 <input v-model="mobile" type="tel" ref="mobile" maxlength="13" @keyup="inputMobile" @paste="inputMobile" />
 </p>
 <p>
 银行卡号：
 <input v-model="card" type="text" @keyup="inputCard" @paste="inputCard" />
 </p>
 </div>
</template>

<script>
 export default {
 data() {
 return {
 mobile: '',
 card: ''
 }
 },
 methods: {
 inputMobile() {
 let value = this.mobile.replace(/\D/g, '').substr(0, 11) // 不允许输入非数字字符，超过11位数字截取前11位
 let len = value.length
 if (len > 3 && len < 8) {
  value = value.replace(/^(\d{3})/g, '$1 ')
 } else if (len >= 8) {
  value = value.replace(/^(\d{3})(\d{4})/g, '$1 $2 ')
 }
 this.mobile = value
 },
 inputCard() {
 this.card = this.card.replace(/\D/g, '') // 不允许输入非数字字符
 this.card = this.card.replace(/(\d{4})(&#63;=\d)/g, '$1 ') // 4位一组，非获取匹配最后一组数字，避免删除到空格时会马上自动补齐
 }
 }
 } 
</script>

<script>
 export default {
 data () {
 return {
 mobile: '',
 card: ''
 }
 },
 methods: {
 inputMobile (e) {
 this.formatMobile(e)
 this.mobile = this.$refs.mobile.value
 },
 formatMobile (e) {
 let val = this.$refs.mobile.value // 不可直接用this.mobile，第一方便提取该方法降低代码耦合度，第二直接用this.mobile,在输入汉字时按下shift按键会导致无法再输入和删除内容
 let selStart = this.$refs.mobile.selectionStart // 选中区域左边界位置
 let mobileLen = val.length
 let value = this.getValue(e, val).substr(0, 11) // 获取输入/粘贴内容,并截取前11位
 let len = value.length
 if (len > 3 && len < 8) {
  value = value.replace(/^(\d{3})/g, '$1 ')
 } else if (len >= 8) {
  value = value.replace(/^(\d{3})(\d{4})/g, '$1 $2 ')
 }
 this.$refs.mobile.value = value
 if (selStart !== mobileLen) {
  if (selStart === 3) {
  selStart++
  }
  // 设置光标位置
  this.$refs.mobile.selectionStart = this.$refs.mobile.selectionEnd = selStart
 }
 },
 getValue(e, val) {
 let value = ''
 if (e.type === 'keyup') {
  value = val.replace(/\D/g, '')
 } else if (e.type === 'paste') {
  // window.clipboardData：IE浏览器获取剪贴板数据对象
  // event.clipboardData：Chrome, Firefox, Safari获取剪贴板数据对象
  let clipboardData = event.clipboardData || window.clipboardData;
  value = clipboardData.getData('Text'); // 获取剪贴板text格式的数据
  value = value.replace(/\D/g, '')
 }
 return value
 }
 }
 }
</script>