JS实现放大镜效果

<!DOCTYPE html>
<html lang="en">
 <head>
  <meta charset="UTF-8">
  <title>JS实现放大镜效果</title>
  <style>
   #small{
    width: 700px;
    height: 340px;
    position: absolute;
    left: 70px;
    top: 100px;
   }
   #small img{
    width: 100%;
    height: 100%;
   }
   #mark{
    width: 200px;
    height: 200px;
    
    position: absolute;
    opacity: 0.5;
    filter: alpha(opacity=50);
    left: 0px;
    top: 0px;
    display: none;
   }
   #big{
    width: 400px;
    height: 400px;
    border: 1px solid black;
    left: 800px;
    top: 100px;
    position: absolute;
    overflow: hidden;
    display: none;
   }
   #big img{
    width: 1400px;
    height: 680px;
    position: absolute;
    left: 0px;
    top: 0px;
   }
  </style>
  <script>
   window.onload = function(){
    var oSmall = document.getElementById("small");
    var oBig = document.getElementById("big");
    var oMark = document.getElementById("mark");
    var oBigImg = oBig.getElementsByTagName("img")[0];
 
    oSmall.onmouseover = function(){
     oMark.style.display = "block";
     oBig.style.display = "block";
    }
    oSmall.onmouseout = function(){
     oMark.style.display = "none";
     oBig.style.display = "none";
    }
    oSmall.onmousemove = function(ev){
     var e = ev || window.event;
     var l = e.clientX - oSmall.offsetLeft - 100;
     if(l <= 0){
      l = 0;
     }
     if(l >= (700-200)){
      l = 500;
     }
     var t = e.clientY - oSmall.offsetTop - 100;
     if(t <= 0){
      t = 0;
     }
     if(t >= (340-200)){
      t = 140;
     }
     oMark.style.left = l + 'px';
     oMark.style.top = t + 'px';
 
     /* 右边图片移动方向与左边图片方向相反且成倍数移动 */
     oBigImg.style.left = l * -2 + 'px';
     oBigImg.style.top = t * -2 + 'px';
 
    }
   }
  </script>
 </head>
 <body>
  <div id="small">
   <img src="/*照片路径*/" alt="怎么回事">
   <div id="mark"></div>
  </div>
  <div id="big">
   <img src="/*照片路径*/" alt="怎么回事">
  </div>
 </body>
</html>
JS实现放大镜效果

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