van-dialog 点击confirm确定时如果不满足条件则不允许关闭

    <van-dialog
      v-model="showDialog"
      @confirm="confirmFn"
      @cancel="showDialog = false"
      title="添加故障现象"
      show-cancel-button
      :before-close="onBeforeClose"
    >
      <div class="p10">
        <van-field
          v-model="faultPhenomenon"
          placeholder="请输入"
          clearable
          :rules="[{ required: true, message: '请输入故障现象' }]"
        />
      </div>
    </van-dialog>

    onBeforeClose (action, done) {
      // 点击了确定按钮
      if (action === "confirm") {
        if (this.faultPhenomenon == '') {
          this.$toast.fail('请输入故障现象');
          return
        }
        // if()...也可以加入一些条件
        return done(false);//直接return它即可阻止
      }
      // 点击了取消按钮
      else {
        done(true); //关闭弹窗, true可以省略
      }
    },
    // 确定添加故障现象
    confirmFn () {

    },