JavaScript实现商品放大镜效果

<style>
        .small{
            position: relative;
            width: 400px;
            height: 450px;
            border: 1px solid #ccc;
        }
        .small img{
            width: 100%;
            height: 100%;
        }
        .small .mask{
            position: absolute;
            left: 0;
            top: 0;
            width: 300px;
            height: 300px;
            background-color: rgba(0, 255, 0, .2);
        }
        .big{
            position: absolute;
            left: 450px;
            top: 8px;
            width: 550px;
            height: 550px;
            border: 1px solid #ccc;
            overflow: hidden;
            display: none;
        }
        .big img{
            position: absolute;
            left: 0;
            top: 0;
        }
    </style>
 
<body>
    <div class="small">
        <img src="./img/small.jpg">
        <div class="mask"></div>
    </div>
    <div class="big">
        <img src="./img/big.jpg">
    </div>
</body>

<script>
        var small=document.querySelector('.small');
        var mask=document.querySelector('.mask');
        var big=document.querySelector('.big');
        var bigImg=document.querySelector('.big>img');
        // 拿到大图的宽高
        var bigWidth=bigImg.offsetWidth;
        var bigHeight=bigImg.offsetHeight;
 
        // 
        function move(e){
            var x=e.pageX - this.offsetLeft;
            var y=e.pageY - this.offsetTop;
            console.log(x,y);
            // 移动遮罩位置
            var maskHeight = mask.offsetHeight/2;
            var maskWidth = mask.offsetWidth/2;
            mask.style.left = x - maskWidth+'px';
            mask.style.top = y - maskHeight+'px';
 
        // 限制遮罩的移动范围
            // console.log('mask.offsetTop',mask.offsetTop);
            // console.log('mask.offsetLeft',mask.offsetLeft);
            var maxLeft=small.offsetWidth - mask.offsetWidth;
            if(mask.offsetTop<0){
                mask.style.top=0;
            }
            if(mask.offsetLeft > small.offsetWidth - mask.offsetWidth){
                mask.style.left =maxLeft+'px';
            }
            if(mask.offsetLeft<0){
                mask.style.left = 0;
            }
            if(mask.offsetTop > small.offsetHeight - mask.offsetHeight){
                mask.style.top = small.offsetHeight - mask.offsetHeight + 'px';
            }
 
        // bigImg 大图  big  大盒子     大图的移动
        // (bigImg.offsetWidth - big.offsetWidth) / (samll.offsetWidtth - mask.offsetWidth)
        //   大图的最大移动距离  = - 遮罩的移动距离 * 大图的最大距离 / 遮罩的最大移动距离
            bigImg.style.left = -mask.offsetLeft*(bigImg.offsetWidth - big.offsetWidth) / (small.offsetWidth - mask.offsetWidth)+"px";
            bigImg.style.top = -mask.offsetTop*(bigImg.offsetHeight - big.offsetHeight) / (small.offsetHeight - mask.offsetHeight)+"px";
        }
       
        // 小图上移动遮罩
        small.addEventListener('mousemove',move);
        small.addEventListener('mouseover',function(){
            big.style.display='block';
            mask.style.display='block';
        })
        small.addEventListener('mouseout',function(){
            big.style.display='none';
            mask.style.display='none';
        })
</script>