微信小程序开发上拉加载如何实现

onReachBottom() {        let isPush = this.data.index,
            val = this.data.inputVal;
        this.setData({
            isBtnShow: true
        });        if (isPush ==1) {            let num = this.data.limitIndex;
            this.setData({                limitIndex: num+1
            })
        //关于上拉加载的性能优化            setTimeout(()=>{
                    // 给后端传下拉刷新的次数+1
                    const data = {                        limitIndex: this.data.limitIndex
                    };
                    utils.sendRequest(api.AllGoodsUrl, data, this.handleReachBottom.bind(this));
            },1500)
        };        if (val != '') {            setTimeout(()=>{                let num = this.data.limitIndex;
                    this.setData({                        limitIndex: num+1
                    })
                    // 给后端传下拉刷新的次数+1
                    const data = {                        limitIndex: this.data.limitIndex,
                         data:{
                            name: this.data.inputVal,
                        }
                    };
                    utils.sendRequest(api.AllGoodsUrl, data, this.handleLoadMore.bind(this));
            },1500)
        };
    },