当电量少于百分之20的时候，字体显示红色

success: function(res) {
        const carList = res.data.list;
        for (let i = 0; i < carList.length; i++){
          if (carList[i].battery < 21){
            carList[i].batStyle = "color:red";
          }
        }
        that.setData({
          carList: res.data.list,
        })
        that.setData({
          leader: res.data.leader,
        })
        if (res.data.list.length>0){
          that.setData({
            back:""
          })
        }
      }