1   // 背景图片的缩放
2           let scale = 1
3           const percent = Math.abs(newY/this.imageHeight)//这么计算，图片的高度相当于增加了newY;
4           if(newY > 0){//向下拉的时候
5             scale = 1 + percent
6           }
7           this.$refs.bgImage.style['transform'] = `scale(${scale})`
8           this.$refs.bgImage.style['webkittransform']  = `scale(${scale})`
9         }