handler(event){let mask =this.$refs.mask;let big =this.$refs.big;let left = event.offsetX - mask.offsetWidth /2;let top = event.offsetY - mask.offsetHeight /2;// 添加约束范围if(left <=0) left =0;if(left >= mask.offsetWidth) left = mask.offsetWidth;if(top <0) top =0;if(top >= mask.offsetHeight) top = mask.offsetHeight;// 修改元素的left/top属性值
mask.style.left = left +'px';
mask.style.top = top +'px';
big.style.left =-2* left +'px';
big.style.top =-2* top +'px';}