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成品镇楼：
这个其实不难，首先要搞清楚offsetx，clientx，pagex，screenx是什么，没搞清楚的想细看的可以参考一下这个文章进行学习。大致就是这样，借鉴博主的图：
以及eventX的区别，作为扩充：
下面进入正题：
首先写结构和默认样式：
结构就三个东西：小图大图和放大镜（遮罩层）
注意大图的样式应该为固定定位，且大图img的宽要大于包裹它的div，并设置div溢出隐藏。
<div id="box">
<div id="smallbox">
<div id="small">
<img src="http://img10.360buyimg.com/n1/jfs/t1/131093/6/11646/193625/5f7d1a70Ed4063f40/3707516b1f09b373.jpg" alt="">
</div>
<div id="mask"></div>
</div>
<div id="big">
<img src="http://img10.360buyimg.com//n0/jfs/t1/131093/6/11646/193625/5f7d1a70Ed4063f40/3707516b1f09b373.jpg" alt="">
</div>
<span>
我是底部内容
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</span>
</div>
*{
margin: 0;
padding: 0;
}
#box{
overflow: hidden;
}
#smallbox,#big{
float: left;
}
#smallbox{
width: 400px;
position: relative;
}
#small,img{
width: 100%;
}
#mask{
position: absolute;
width: 150px;
height: 150px;
background-color: rgba(255, 255, 0, 0.211);
top: 0;
left: 0;
display: none;
}
#big{
display: none;
/* 加绝对定位这样才能不遮挡放大图下的内容 */
position: absolute;
width: 600px;
height: 600px;
left: 400px;
top: 0px;
z-index: 999;
border: 1px solid rgba(0, 0, 0, 0.095);
background-color: white;
overflow: hidden;
}
#big img{
position: absolute;
top: 0;
left: 0;
width: 1000px;
}
就是控制：
先控制遮罩层和大图的显示隐藏，再移动遮罩层最后设置大图移动：
注意在计算大图移动的位移时应该是按比例计算得出的。
$('#smallbox').mouseenter(function(e){
$('#mask').css('display','block')
$('#big').css('display','block')
})
$('#smallbox').mouseleave(function(e){
$('#mask').css('display','none')
$('#big').css('display','none')
})
$('#smallbox').mousemove(function(e){
console.log(e.clientX,e.clientY);
//距离浏览器上方和左边的距离，这里因为smallbox的top，left为0所以直接取鼠标距离盒子左上都为client，如果盒子距离左边上面有边距则剪掉top和left即可
let x = e.clientX
let y = e.clientY
//因为mask是以左上角为顶点，要让鼠标在mask中心则需减去mask一半的宽高
$('#mask').css({'left':x-75+'px','top':y-75+'px'})
//大图的移动，相当于#big为可视区域，故图片应为反方向移动取负值，移动距离是按比例的移动即：
//x-75：400 = m：600=====》m=1.5*（x-75） m为大图移动的距离
$('#big img').css({'left':-1.5*(x-75)+'px','top':-1.5*(y-75)+'px'})
})
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>京东放大镜</title>
<style>
*{
margin: 0;
padding: 0;
}
#box{
overflow: hidden;
}
#smallbox,#big{
float: left;
}
#smallbox{
width: 400px;
position: relative;
}
#small,img{
width: 100%;
}
#mask{
position: absolute;
width: 150px;
height: 150px;
background-color: rgba(255, 255, 0, 0.211);
top: 0;
left: 0;
display: none;
}
#big{
display: none;
/* 加绝对定位这样才能不遮挡放大图下的内容 */
position: absolute;
width: 600px;
height: 600px;
left: 400px;
top: 0px;
z-index: 999;
border: 1px solid rgba(0, 0, 0, 0.095);
background-color: white;
overflow: hidden;
}
#big img{
position: absolute;
top: 0;
left: 0;
width: 1000px;
}
</style>
</head>
<body>
<div id="box">
<div id="smallbox">
<div id="small">
<img src="http://img10.360buyimg.com/n1/jfs/t1/131093/6/11646/193625/5f7d1a70Ed4063f40/3707516b1f09b373.jpg" alt="">
</div>
<div id="mask"></div>
</div>
<div id
