Realization of native js magnifying glass

The effect is as follows: the
Insert picture description here
code is as follows: implemented with native js, the comments are in the code, if you don’t understand, you can leave a message to discuss
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>放大镜</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box{
            margin-top: 50px;
            margin-left: 100px;
        }
        .small{
            cursor: all-scroll
        }
    .small img{
        width: 400px;
        height: 500px;
    }
    .small,
    .big{
        width: 400px;
        height: 500px;
        vertical-align: top;
        position: relative;
        display: inline-block;
    }
    .big{
       overflow: hidden;
    }
    .big img{
        display: none;
        position: absolute;
        width: 800px;
        top: 0;
        left: 0;
    }
    .zhezhaoceng{
        width: 150px;
        height: 150px;
        background:rgba(0, 0, 0,.3);
        position: absolute;
        top: 0;
        left:0;
        z-index: 999;
    }
    </style>
</head>
<body>
    <div class="box">
        <!-- 原图 -->
        <div class="small">
            <img src="./images/small.png" alt="" class="smallimg">
            <!-- //遮罩层 -->
            <div class="zhezhaoceng"></div>
        </div>
         <!-- 放大后-->
         <div class="big">
             <img src="./images/big.jpg" alt="" class="bigimg">
         </div>
    </div>
    <script>
    var small=document.getElementsByClassName('small')[0];
    var big=document.getElementsByClassName('big')[0];
    var bigimg=document.getElementsByClassName('bigimg')[0];
    var smallimg=document.getElementsByClassName('smallimg')[0];
    var zhezhaoceng=document.getElementsByClassName('zhezhaoceng')[0];
    small.onmouseover=function(){
        bigimg.style.display='block';
        document.onmousemove=function(e){
            var e=e||window.event;
            var movingY=e.pageY-small.offsetTop-zhezhaoceng.offsetHeight/2;
            var movingX=e.pageX-small.offsetLeft-zhezhaoceng.offsetWidth/2;
            //判断是否超出界限
            movingY=movingY<0?0:movingY;
            movingY=movingY>small.offsetHeight-zhezhaoceng.offsetHeight?small.offsetHeight-zhezhaoceng.offsetHeight:movingY;
            movingX=movingX<0?0:movingX;
            movingX=movingX>small.offsetWidth-zhezhaoceng.offsetWidth?small.offsetWidth-zhezhaoceng.offsetWidth:movingX;
            // console.log(movingY);
            // console.log(movingX);
            zhezhaoceng.style.top=movingY+'px';
            zhezhaoceng.style.left=movingX+'px';
            //设置右边图片移动
            //遮挡层的移动距离/遮挡层的最大移动距离=大图的移动距离/大图的最大移动距离
            //大图的移动距离=遮挡层的移动距离*大图的最大移动距离/遮挡层的最大移动距离
            //大图最大移动距离
            var bigMaxY=bigimg.offsetHeight-big.offsetHeight;
            var bigMaxX=bigimg.offsetWidth-big.offsetWidth
            //遮罩层最大移动距离
            var zheY=smallimg.offsetHeight-zhezhaoceng.offsetHeight;
            var zheX=smallimg.offsetWidth-zhezhaoceng.offsetWidth;
			//计算大图移动距离
            var bigimgLeft=movingX*bigMaxX/zheX;
            var bigimgTop=movingY*bigMaxY/zheY;
            //赋值
            bigimg.style.top=-bigimgTop+'px';
            bigimg.style.left=-bigimgLeft+'px';
        }
    }
    small.onmouseout=function(){
        bigimg.style.display='none';
    }
    
    </script>
</body>
</html>
Realization of native js magnifying glass

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