原生js仿淘宝网商品放大镜效果

效果图：（实例图片由自己添加）

代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>仿淘宝放大镜特效</title>
 <style type="text/css">
 *{margin: 0;padding: 0;}
 #demo{width:350px;height:350px;border: 1px solid #000;position:relative;margin:100px;}
 #smil_box{width: 350px;height: 350px;position:relative;}
 #mask{width:175px;height: 175px;background:rgba(255,255,0,0.4);position:absolute;top:0;left:0;display:none;cursor:move;}
 #big_box{width: 400px;height: 400px;position:absolute;top:0;left:360px;border: 1px solid #000;overflow:hidden;display:none;}
 #big_box img{position:absolute;top:0;left:0;}
 </style>
</head>
<body>
 <div id="demo">
 <div id="smil_box">
 <img src="http://www.qdfuns.com/misc.php?mod=attach&genre=editor&aid=193662baf63738c68b594f3ec920769f" height="350" width="350" alt="">
 <div id="mask"></div>
 </div>
 <div id="big_box">
 <img src="http://www.qdfuns.com/misc.php?mod=attach&genre=editor&aid=3e8b3554eb90dd13fa0f82465ac6d382" height="800" width="800" alt="" id="big_img">
 </div>
 </div>
</body>
<script type="text/javascript">
 (function(window){
 function $(id){
 return document.getElementById(id);
 };
 // 获取对象
 var demo = $("demo"),smilBox = $("smil_box"),mask = $("mask"),bigImg = $("big_img"),bigBox = $("big_box");
 // smilBox的hover事件
 smilBox.onmouseover = function(){
 mask.style.display = "block";
 bigBox.style.display = "block";
 };
 smilBox.onmouseout = function(){
 mask.style.display = "none";
 bigBox.style.display = "none";
 };
 // 鼠标移动事件
 smilBox.onmousemove = function(event){
 var event = event || window.event;
 // 获取鼠标在页面上的坐标
 var pageX = event.pageX || event.clientX + document.documentElement.scrollLeft;
 var pageY = event.pageY || event.clientY + document.documentElement.scrollTop;
 // mask的位置坐标
 var boxX = pageX - demo.offsetLeft;
 var boxY = pageY - demo.offsetTop;
 var maskX = boxX - mask.offsetWidth / 2;
 var maskY = boxY - mask.offsetHeight / 2;
 // 限制mask的移动范围
 if( maskX < 0 ){
 maskX = 0;
 };
 if( maskX > smilBox.offsetWidth - mask.offsetWidth){
 maskX = smilBox.offsetWidth - mask.offsetWidth;
 };
 if( maskY < 0 ){
 maskY = 0;
 };
 if( maskY > smilBox.offsetHeight - mask.offsetHeight){
 maskY = smilBox.offsetHeight - mask.offsetHeight;
 };
 // 黄色遮罩层的位置坐标
 mask.style.top = maskY + "px";
 mask.style.left = maskX + "px";
 // 大图片移动的比例
 var prop = ( bigImg.offsetWidth - bigBox.offsetWidth ) / (smilBox.offsetWidth - mask.offsetWidth);
 // 大图片的坐标
 var bigImgX = prop * maskX;
 var bigImgY = prop * maskY;
 bigImg.style.top = -bigImgY + "px";
 bigImg.style.left = -bigImgX + "px";
 }
 })(window)
</script>
</html>

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