elementui input框點擊觸發placeholder清空

<el-form-item prop="tel" class="topform">
              <el-input  maxlength="11" v-model.number="ReginForm.tel" @focus="blurSearchFor()" @blur="blurSear" :placeholder="placeholder"></el-input>
</el-form-item>

data{
   return{
       placeholder:'請您輸入手機號'
   }
}

methods:{
        //獲取焦點時觸發
        blurSearchFor(){
          console.log(this.placeholder)
          if(this.placeholder=='請您輸入手機號'){
              this.placeholder='';
          }
      },
        //失去焦點時觸發
      blurSear(){
          this.placeholder='請您輸入手機號';
      }
}