<span style:"color:red;visibility:hidden" ref='input1'>*</span>
<el-input v-model="uname" @blur="checkIsNull"></el-input>
<span style:"color:red;visibility:hidden" ref='input2'>*</span>
<el-input v-model="upwd" @blur="checkIsNull"></el-input>
<script>
  checkIsNull(param) {
    if (param == 1) {
       if (uname == "") {
         this.$refs.input1.style.visibility = 'visible'
           } else {
            this.$refs.input1.style.visibility = 'hidden'
          }

    if (param == 2) {
       if (upwd == "") {
          this.$refs.input2.style.visibility = 'visible'
            } else {
              this.$refs.input3.style.visibility = 'hidden'
          }
    }
</script>