原生JavaScript实现放大镜效果完整代码

<!DOCTYPE HTML>
<html>
<head>
<title>js放大镜效果</title>
<meta http-equiv="content-type" content="text/html;charset=utf-8"/>
<style>
*{
margin:0px;
padding:0px;
border:none;
list-style:none;
}
#box{
margin:80px auto;
width: 352px;
}
#box p
{
width: 350px;
height: 350px;
border: 1px solid #ddd;
margin-bottom: 5px; 
}
#box p img
{
width:350px;
height:350px;
}
#box h1
{
width: 352px;
height: 54px;
overflow:hidden; 
position:relative;
}
#box h1 div
{
width:310px;
height: 54px;
margin:0px auto;
position:relative;
}
#box h1 div ul
{
position:absolute;
left: 0px;
top: 0px;
}
#box h1 ul li
{
width: 62px; 
float: left;
}
#box h1 ul li img
{
width: 50px;
height: 50px;
padding: 1px;
border: 1px solid #CECFCE;
}
#box h1 img.hoveredThumb{
border: 2px solid #e4393c;
padding: 0;
}
/*中等大小的图片显示区域*/
p#medImgBox{
position: relative;
}
#jing{
position: absolute;
left: 0;
top: 0;
width: 175px;
height: 175px;
border-radius:50%;
background: #ffd;
opacity: 0.7;
display: none;
}
/*悬于图片/jing上方的专用于接收鼠标移动事件的
一个完全透明的层*/
#medImgBox #mian{
display: block;
position: absolute;
width: 100%;
height: 100%;
top: 0;
left: 0;
cursor: move;
opacity: 0;
}
/**
大图显示区域
**/
#largeImgBox{
position:absolute;
width: 175px;
height: 175px;
border-radius:50%;
border: 1px solid #faa;
top: 0px;
left: 352px; 
overflow: hidden;
display: none;
}
#largeImg{
display: none;
position: absolute;
}
</style> 
</head>
<body >
<div id="box">
<p id="medImgBox">
<img id="mediumImg" src="images/product-s1-m.jpg" />
<span id="jing"></span>
<span id="mian"></span>
<span id="largeImgBox">
<img id="largeImg"/>
</span>
</p>
<h1>
<div>
<ul id="list">
<li><img src="images\product-s1.jpg" /></li>
<li><img src="images\product-s2.jpg" /></li>
<li><img src="images\product-s3.jpg" /></li>
<li><img src="images\product-s4.jpg" /></li>
<li><img src="images\product-s1.jpg" /></li>
</ul>
</div>
</h1>
</div>
<script>
var imgList = document.querySelectorAll('#box ul li img');
for(var i=0; i<imgList.length; i++){
var img = imgList[i];
img.onmouseover = changeThumbImg;
}
function changeThumbImg(){
var previousHovered = document.querySelector('.hoveredThumb');
if(previousHovered==null){
this.className = 'hoveredThumb'; 
changeMediumImg(this.src); //修改中等图片的src
}else if(previousHovered!=this){
previousHovered.removeAttribute('class');
this.className = 'hoveredThumb';
changeMediumImg(this.src); //修改中等图片的src
}
}
function changeMediumImg(thumbSrc){
var dotIndex = thumbSrc.lastIndexOf('.');
var prefix = thumbSrc.substring(0, dotIndex);
var suffix = thumbSrc.substring(dotIndex);
var mediumSrc = prefix + '-m'+suffix;
document.getElementById('mediumImg').src = mediumSrc;
}
/**
为放大镜jing添加鼠标移动事件
**/
document.querySelector('#mian').onmousemove = 
function(event){
var x = event.offsetX; //事件相对于事件源的偏移量
var y = event.offsetY; 
var jing = document.getElementById('jing'); 
var w = jing.offsetWidth; //jing的宽和高
var h = jing.offsetHeight;
var left = x<w/2 ? 0 : (x-w/2);
var top = y<h/2 ? 0 : (y-h/2);
if(x>(w*2-w/2)){
left = w*2 - w;
}
if(y>(h*2-h/2)){
top = h*2 - h;
}
jing.style.left = left+'px';
jing.style.top = top+'px';
//修改大图的位置/
var largeImg = document.getElementById('largeImg');
largeImg.style.left = (-left*largeImg.width/350) + 'px';
largeImg.style.top = (-top*largeImg.height/350)+'px';
}
document.querySelector('#mian').onmouseover = function(){
//显示jing
var jing = document.getElementById('jing');
jing.style.display = 'block';
var largeImgBox = document.getElementById('largeImgBox');
largeImgBox.style.display = 'block';
//获取当前要显示的大图的src
var src = document.querySelector('#mediumImg').src;
var dotIndex = src.lastIndexOf('.');
var prefix = src.substring(0, dotIndex-2);
var suffix = src.substring(dotIndex);
src = prefix + '-l'+ suffix;
var largeImg = document.getElementById('largeImg');
largeImg.src = src;
largeImg.style.display='block';
}
document.querySelector('#mian').onmouseout = 
function(){
//除去jing
var jing = document.getElementById('jing');
jing.style.display = 'none';
//除去大图显示区
document.getElementById('largeImgBox').style.display = 'none';
}
</script>
</body>
</html>