JavaScript如何实现手机号码3-4-4格式并控制新增和删除时光标的位置

// An highlighted block
 

// javascript
onInput(){
 val = this.value.replace(/\D/g, '').substring(0, 11);
 const nowIndex = this.getCursortPosition(this.$refs.inputRef);
 if (valueLen > 3 && valueLen < 8) {
 this.value = `${val.substr(0, 3)} ${val.substr(3)}`;
 } else if (valueLen >= 8) {
 this.value = `${val.substr(0, 3)} ${val.substr(
  3,
  4
  )} ${val.substr(7)}`;
 } else {
 this.value = val;
 }
 // 重新赋值之后设置光标的位置
this.setCurIndex(nowIndex, this.curInputObj.value);
},

 getCursortPosition(element) {
 let CaretPos = 0;
 if (document.selection) {
 // 支持IE
 element.focus();
 const Sel = document.selection.createRange();
 Sel.moveStart('character', -element.value.length);
 CaretPos = Sel.text.length;
 } else if (element.selectionStart || element.selectionStart === '0'){
 // 支持firefox
 CaretPos = element.selectionStart;
 }
 return CaretPos
 },

 setCurIndex(nowIndex, value) {
 const len = value.length;
 setTimeout(() => {
 let pos = nowIndex;
 // 新增操作
 if (len > this.oldLen) {
  if (nowIndex === 4 || nowIndex === 9) {
  pos += 1;
  }
 } else if (len > this.oldLen) {
  // 删除操作
  if (nowIndex === 4 || nowIndex === 9) {
  pos -= 1;
  }
 }
 this.$refs.inputRef.selectionStart = pos;
 this.$refs.inputRef.selectionEnd = pos;
 this.oldLen = this.curInputObj.value.length;
 }, 0);
 },