功能需求：
1、分为三个模块
2、鼠标经过小图片盒子，黄色的遮挡层和大图片盒子显示，离开隐藏两个盒子功能
3、黄色的遮挡层跟随着鼠标移动
4、移动黄色遮挡层，大图片跟随着移动
大图片移动距离=（遮挡层移动距离*大图片最大移动距离）/ 遮挡层最大移动距离
<style>
body,
div {
margin: 0;
padding: 0;
}
.product {
position: relative;
width: 400px;
height: 400px;
margin: 50px 0 0 20px;
border: 1px solid #000;
}
.preview_img img {
width: 300px;
height: 300px;
margin: 50px 50px;
}
.mask {
position: absolute;
display: none;
top: 20px;
left: 30px;
width: 80px;
height: 80px;
background-color: yellow;
opacity: 0.5;
cursor: move;
}
.big {
position: absolute;
display: none;
left: 410px;
top: 0;
width: 500px;
height: 500px;
z-index: 999;
overflow: hidden;
}
.big img {
position: absolute;
top: 0;
left: 0;
width: 400px;
height: 400px;
}
</style>
<!-- 引入js文件 -->
<script src="detail.js"></script>
</head>
<body>
<div class="product">
<div class="preview_img">
<img src="images/xs.jpg" alt="" />
<div class="mask"></div>
<div class="big">
<img src="images/xs.jpg" alt="" class="bigImg" />
</div>
</div>
</div>
</body>
JS页面
//页面预加载
window.addEventListener("load", function () {
var preview_img = document.querySelector(".preview_img");
var mask = document.querySelector(".mask");
var big = document.querySelector(".big");
//1.鼠标经过 preview_img 就显示和隐藏 mask 遮挡层 和 big 大盒子
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";
});
//把鼠标坐标给遮挡层是不合适的，因为遮挡层坐标以父盒子为准
preview_img.addEventListener("mousemove", function (e) {
//（1）先计算出鼠标在盒子内的坐标
var x = e.pageX - this.offsetLeft;
var y = e.pageY - this.offsetTop;
//（2）减去盒子高度宽度的一半
//（3）mask 移动的距离
var maskX = x - mask.offsetWidth / 2;
var maskY = y - mask.offsetHeight / 2;
//(4)如果坐标小于0 就让他停在 0 的位置(即超出盒子范围就停止)
var egdeX = preview_img.offsetWidth - mask.offsetWidth;
var egdeY = preview_img.offsetHeight - mask.offsetHeight;
if (maskX <= 0) {
maskX = 0;
} else if (maskX >= egdeX) {
maskX = egdeX;
}
if (maskY <= 0) {
maskY = 0;
} else if (maskY >= egdeY) {
maskY = egdeY;
}
mask.style.left = maskX + "px";
mask.style.top = maskY + "px";
//大图片的移动距离 = 遮挡层移动距离*大图片最大移动距离 / 遮挡层的最大移动距离
var bigImg = document.querySelector(".bigImg");
//大图片最大移动距离
var bigMax = bigImg.offsetWidth - big.offsetWidth;
//大图片的移动距离 x y
var bigX = (maskX * bigMax) / egdeX;
var bigY = (maskY * bigMax) / egdeY;
bigImg.style.left = -bigX + "px";
bigImg.style.top = -bigY + "px";
});
});
