!DOCTYPE html>
html lang="en">
head>
 meta charset="UTF-8">
 title>放大镜/title>
 style>
 *{margin:0;padding: 0;}
 #warp{width: 1184px;height:500px;margin:50px auto 0;background-color: #ccc;overflow: hidden;padding: 10px;position: relative;}
 #warp #minbox{width: 350px;height: 350px;float: left;position: relative;}
 #maxbox{width: 400px;height: 400px;position: absolute;left: 380px;overflow: hidden;display: none;}
 #maxbox img{width: 800px;height: 800px;position: absolute;}
 #con{float: left;margin-left: 20px;}
 #meng{width: 175px;height: 175px;position: absolute;background-color:yellow;opacity:0.4;filter:alpha(opacity=40);left: 0;top: 0;display: none;}
 /style>
/head>
body>
 div id="warp">
 div id="minbox">
  img src="images/min.jpg" alt="">
  p id="meng">/p>
 /div>
 div id="maxbox">
  img src="images/max.jpg" alt="">
 /div>
 div id="con">
  img src="images/msg.png" alt="">
 /div>
 /div>
 script>
 var minbox=document.getElementById('minbox');
 var meng=document.getElementById('meng');
 var maxbox=document.getElementById('maxbox');
 var maximg=maxbox.getElementsByTagName('img')[0];
 var minimg=minbox.getElementsByTagName('img')[0];
 function offsetTL(obj){
  var ofL=0,ofT=0;
  while(obj){
  ofL+=obj.offsetLeft+obj.clientLeft;
  ofT+=obj.offsetTop+obj.clientTop;
  obj=obj.offsetParent;
  }
  return{left:ofL,top:ofT};
 }
 minbox.onmousemove=function(e){
  var e=e||window.event;
  meng.style.display='block';
  maxbox.style.display='block';
  var niubi1=e.clientX-offsetTL(minbox).left-meng.clientWidth/2;//蒙板的X坐标
  var niubi2=e.clientY-offsetTL(minbox).top-meng.clientHeight/2;//蒙板的Y坐标
  var bili=maximg.clientWidth/minimg.clientWidth;
  if (niubi1=0) {
  niubi1=0;
  }else if (niubi1>=minbox.clientWidth-meng.clientWidth) {
  niubi1=minbox.clientWidth-meng.clientWidth;
  }
  if (niubi2=0) {
  niubi2=0;
  }else if (niubi2>=minbox.clientHeight-meng.clientHeight) {
  niubi2=minbox.clientHeight-meng.clientHeight;
  }
  console.log(niubi1);
  console.log(niubi2);
  meng.style.left=niubi1+'px';
  meng.style.top=niubi2+'px';
  maximg.style.left=-parseInt(meng.style.left)*bili+'px';
  maximg.style.top=-parseInt(meng.style.top)*bili+'px';
 }
 minbox.onmouseout=function(){
  meng.style.display='none';
  maxbox.style.display='none';
 }
 /script>
/body>
/html>