JavaScript实现简单放大镜效果

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>手机详情页</title>
    <!-- <link rel="stylesheet" href="css/detail.css" >
    <script src="js/detail.js"></script> -->
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        .detail-content {
            width: 1200px;
            margin: 0 auto;
        }
        
        img {
            border: 0;
            vertical-align: middle;
        }
        
        .preview_img {
            position: relative;
            width: 400px;
            height: 400px;
            margin-top: 30px;
            border: 1px solid #ccc;
        }
        
        .preview_img img {
            width: 100%;
            height: 100%;
        }
        
        .mask {
            display: none;
            position: absolute;
            top: 0;
            left: 0;
            width: 300px;
            height: 300px;
            background-color: pink;
            opacity: .5;
            cursor: move;
        }
        
        .big {
            display: none;
            position: absolute;
            top: 0;
            left: 410px;
            width: 500px;
            height: 500px;
            border: 1px solid #ccc;
            background-color: pink;
            z-index: 999;
            overflow: hidden;
        }
        
        .big img {
            position: absolute;
            top: 0;
            left: 0;
            width: 800px;
            height: 800px;
        }
    </style>
</head>

<body>
    <div class="detail-content">
        <div class="preview_img">
            <img src="upload/s3.png" alt="">
            <div class="mask"></div>
            <div class="big">
                <img src="upload/big.jpg" alt="" class="bigImg">
            </div>
        </div>
    </div>

    <script>
        var previewImg = document.querySelector('.preview_img');
        var mask = document.querySelector('.mask');
        var big = document.querySelector('.big');
        var bigImg = document.querySelector('.bigImg');

        // 鼠标经过盒子事件
        previewImg.addEventListener('mouseover', function() {
            // 设置遮挡层和放大图显示
            mask.style.display = 'block';
            big.style.display = 'block';
        })

        // 鼠标离开盒子事件
        previewImg.addEventListener('mouseout', function() {
            // 设置遮挡层和放大图隐藏
            mask.style.display = 'none';
            big.style.display = 'none';
        })

        // 鼠标在盒子内移动事件
        previewImg.addEventListener('mousemove', function(e) {
            // 获取鼠标在盒子中的位置
            var x = e.pageX - this.offsetLeft;
            var y = e.pageY - this.offsetTop;

            // 计算出遮挡层的移动值，让鼠标在遮挡层中间位置
            var maskX = x - mask.offsetWidth / 2;
            var maskY = y - mask.offsetHeight / 2;

            // 盒子为正方形，所以只算最大水平方向 X轴 移动值就行，Y轴最大移动值和 X轴 一致
            var maskMax = previewImg.offsetWidth - mask.offsetWidth;

            // 限制遮挡层在盒子内移动
            if (maskX <= 0) {
                maskX = 0;
            } else if (maskX >= maskMax) {
                maskX = maskMax;
            }

            if (maskY <= 0) {
                maskY = 0;
            } else if (maskY >= maskMax) {
                maskY = maskMax;
            }

            mask.style.left = maskX + 'px';
            mask.style.top = maskY + 'px';

            // 计算出放大图的最大移动值，大图水平移动值 = 遮挡层移动值 * 大图最大移动距离 / 遮挡层最大移动距离
            var bigMax = bigImg.offsetWidth - big.offsetWidth;

            var bigX = maskX * bigMax / maskMax;
            var bigY = maskY * bigMax / maskMax;

            bigImg.style.left = -bigX + 'px';
            bigImg.style.top = -bigY + 'px';

        })
    </script>
</body>

</html>