directives: {
  'mtfocus' (el, binding, vnode) {
   let mtinput = el.querySelector('input')
   mtinput.onfocus = function () {
    ...//如果要对节点的数据进行更改,且更改要映射到页面上,则更改可在vnode.context上进行,这样,改完之后,改变就会映射到页面
   }
   mtinput.onblur = function () {
    ...//同上理
   }
  } 
 }

<input ref="inputVal" class="searchInp" type="text" v-model="searchVal" placeholder="搜索标题或内容..." />
<div v-show="searchBtnFlag" class="searchBtn" @click="searchIn">
 <i class="iconfont icon-search1187938easyiconnet"></i> 搜索
</div>

searchIn(){
 this.searchBtnFlag = !this.searchBtnFlag;
 this.$nextTick(function () {
  //DOM 更新了
  this.$refs.inputVal.focus()
 })
},

<input id="inputVal" class="searchInp" type="text" v-model="searchVal" placeholder="搜索标题或内容..." />
<div v-show="searchBtnFlag" class="searchBtn" @click="searchIn">
 <i class="iconfont icon-search1187938easyiconnet"></i> 搜索
</div>

searchIn(){
 this.searchBtnFlag = !this.searchBtnFlag;
 this.$nextTick(function () {
 document.getElementById("inputVal").focus();
 })
},

<input v-bind:autofocus="!searchBtnFlag" class="searchInp" type="text" v-model="searchVal" placeholder="搜索标题或内容..." />
<div v-show="searchBtnFlag" class="searchBtn" @click="searchIn">
  <i class="iconfont icon-search1187938easyiconnet"></i> 搜索
</div>

 searchIn(){
   this.searchBtnFlag = !this.searchBtnFlag;
   this.$nextTick(function () {
  document.getElementById("inputVal").focus();
   })
 },