van-calendar选择单个日期，并且以这种格式传2024-

<van-field label-width="60px" v-model="form.native" label="国籍：" />
              <van-field label-width="60px" readonly clickable  @click="birthdayShow = true" v-model="form.birthday" label="出生年月：" />
              <van-field label-width="60px" v-model="form.poloutlock" label="政治面貌：" />
              <van-calendar v-model="birthdayShow" color='#00CA9D'   @confirm="onConfirmDate" />

    onConfirmDate(data){
      this.birthdayShow = false;
      console.log('日期',data)
      this.form.birthday = `${this.formatDate(data)}`
      console.log('日期字符串',this.form.birthday)
    },
    formatDate(now){
      let year = now.getFullYear();
      let month = now.getMonth() +1;
      let date = now.getDate();
      return year + '-' + month + '-'+date
    }