代码实现：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.preview-img {
position: relative;
height: 398px;
}
.mask {
display: none;
position: absolute;
top: 0;
left: 0;
300px;
height: 300px;
background-color: skyblue;
opacity: .4;
border: 1px solid #ccc;
cursor: move;
}
.big {
overflow: hidden;
display: none;
position: absolute;
top: 0;
left: 410px;
500px;
height: 500px;
background-color: pink;
z-index: 99;
border: 1px solid #ccc;
}
.big img {
position: absolute;
top: 0;
left: 0;
}
</style>
</head>
<body>
<script>
window.addEventListener('load', function() {
var preview_img = document.querySelector('.preview-img');
var mask = document.querySelector('.mask');
var big = document.querySelector('.big');
// 显示与隐藏
preview_img.addEventListener('mouseover', function() {
mask.style.display = 'block';
big.style.display = 'block';
});
preview_img.addEventListener('mouseout', function() {
mask.style.display = 'none';
big.style.display = 'none';
});
// 盒子跟随鼠标移动
preview_img.addEventListener('mousemove', function(e) {
var x = e.pageX - this.offsetLeft;
var y = e.pageY - this.offsetTop;
var maskX = x - mask.offsetWidth / 2;
var maskY = y - mask.offsetHeight / 2;
var maskMax = preview_img.offsetHeight - mask.offsetHeight;
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';
// 大图，根据比例计算坐标
var bigImg = document.querySelector('.bigImg');
var bigMax = bigImg.offsetWidth - big.offsetWidth;
var bigX = bigMax * maskX / maskMax;
var bigY = bigMax * maskY / maskMax;
bigImg.style.left = -bigX + 'px';
bigImg.style.top = -bigY + 'px';
});
});
</script>
<div class="preview-img">
<img src="https://s1.ax1x.com/2020/10/12/027yRg.jpg" alt="">
<div class="mask"></div>
<div class="big">
<img src="https://s1.ax1x.com/2020/10/12/0276zQ.jpg" alt="" class="bigImg">
</div>
</div>
</body>
</html>
实现效果：
