+数量增加方法，我点击按钮，最起码要等一秒数据才在页面上完成更新渲染，控制台是会先打印出‘已更新已渲染’但数据往往是要子啊过一会儿才会增加

add: function (e) {

    db.collection('secShopcart').doc(e.target.dataset.id).update({

      data:{

        count:_.inc(1)

      }

    }).then(res => {

      console.log("已更新")

      var that = this;

      db.collection('secShopcart').get().then(res => {

        that.setData({

          goods: res.data,

          // count:res.data

        })

        this.setCart(res.data) //统计件数与价格

      })

      console.log("已渲染")

    })

  },

 <view wx:for="{{goods}}" wx:key="_id">

      <van-card title='{{item.title}}' desc='{{item.seller}}' price="{{item.price}}" thumb='{{item.image}}'

        num='{{item.count}}'>

        <!-- <view slot="tags">

          <view wx:for="{{item.tags}}"  wx:key="_id" wx:for-index="idx" wx:for-item="tag">

            <view wx:if="{{idx < 2}}">

              <van-tag type="primary">{{tag.name}}</van-tag>

            </view>

          </view>

        </view> -->

        <view slot="footer">

          <van-button size="mini" data-id="{{item._id}}" type="default" plain bind:click="del">-</van-button>

          <van-button size="mini" data-id="{{item._id}}" type="default" plain bind:click="add">+</van-button>

          <van-checkbox class="check" style="display:{{shows}}" name="{{ item._id }}" bind:change="onChange"

            data-id="{{item._id}}">

          </van-checkbox>

        </view>

      </van-card>

    </view>