<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
*{
margin:0;
padding:0;
}
#box{
width: 350px;
height: 350px;
border:1px solid #ccc;
position: relative;
margin:100px;
}
#small{
position: relative;
}
#mask{
width: 100px;
height: 100px;
position: absolute;
top:0;
left:0;
background: rgba(255,255,0,.4);
cursor: move;
display: none;
}
#big{
width: 450px;
height: 450px;
position: absolute;
top:0;
left: 360px;
overflow: hidden;
display: none;
}
#big img{
position: absolute;
top:0;
left:0;
}
</style>
</head>
<body>
<div id="box">
<div id="small">
<div id="mask"></div>
</div>
<div id="big">
</div>
</div>
<script>
// 获取元素
var box = document.getElementById("box");
var small = document.getElementById("small");
var mask = document.getElementById("mask");
var big = document.getElementById("big");
var bigImg = big.querySelector("img");
small.onmouseover = function () {
mask.style.display = "block";
big.style.display = "block";
};
small.onmouseout = function () {
mask.style.display = "none";
big.style.display = "none";
};
small.onmousemove = function (event) {
var e = event ||window.event;
// 获取鼠标位置（可视区域）
var mX = e.clientX;
var mY = e.clientY;
// 计算放大镜的移动范围
var maxLeft = box.offsetWidth - mask.offsetWidth;
var maxTop = box.offsetHeight - mask.offsetHeight;
// 设置临时位置
var tempLeft = mX - box.offsetLeft - mask.offsetWidth / 2;
var tempTop = mY - box.offsetTop - mask.offsetHeight / 2;
// 设置最终位置
var nowLeft = 0;
var nowTop = 0;
if(tempLeft >= maxLeft){
nowLeft = maxLeft;
}else if(tempLeft>0 && tempLeft < maxLeft){
nowLeft = tempLeft;
}
if(tempTop >= maxTop){
nowTop = maxTop;
}else if(tempTop > 0 && tempTop < maxTop){
nowTop = tempTop;
}
// 遮罩跟随鼠标
mask.style.left = nowLeft + "px";
mask.style.top = nowTop + "px";
// 计算移动比例
var ratioX = box.offsetWidth / bigImg.offsetWidth;
var ratioY = box.offsetHeight / bigImg.offsetHeight;
// 大图位置
bigImg.style.left = - nowLeft / ratioX + "px";
bigImg.style.top = - nowTop / ratioY + "px";
}
</script>
</body>
</html>
这种布局方式相对来说更好操作，小图和大图在同一个盒子里；
难点在于获取鼠标在盒子中的位置，不明白的朋友可以自己画图，可以更直观的理解。
再一点就是遮罩移动，大图移动，强调下，移动的不是大图的父级盒子，而是图片本身，根据图片比例移动，比如，遮罩在小图上移动1px，那么在大盒子上移动的就是 1 / 小图 / 大图 。代码中有所体现，如有哪里不清楚，请在下方留言，我会第一时间回复！
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