JS实现图片放大镜功能：原理、代码与常见问题解析

<html>
 <head>
  <meta charset="UTF-8">
  <title>WEBGOD</title>
  <link rel="stylesheet" type="text/css" href="css/bootstrap.min.css"/>
  <script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script>
  <script src="js/bootstrap.min.js" type="text/javascript" charset="utf-8"></script>
  <style type="text/css">
   #warpper{
    margin: 0 auto;
    padding: 0;
    position: relative;
    z-index: 1;
    width: 600px;
    height: 400px;
   }
   .small{
    text-align: center;
   }
   .big{
    display: none;
    clip: rect(200px,900px,600px,300px);
    position: absolute;
    width: 1200px;
    height: 800px;
    top: 50%;
    left:50%;
    transform: translate(-50%,-50%);
   }
   .big img{
    position: absolute;
    width: 600px;
    height: auto;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto;
   }
  </style>
 </head>
 <body>
   
  <div id="warpper">
   <div class="small">
    <img src="img/small_19.jpg"/>
   </div>
   <div class="big">
    <img src="img/img_19.jpg"/>
   </div>
  </div>
  <script type="text/javascript">
   $(function(){
    var x,y,left,top,width,height,imgWidth,imgHeight,rateX,rateY;
    $("#warpper").hover(function(){
     $(".big").css("display","block");
     $(".big img").animate({"width":"1200px"},500);
    },function(){
     $(".big img").animate({"width":"600px"},1);
     $(".big").css("display","none");
    })
    $("#warpper").on("mousemove",function(e){
     x = e.pageX;
     y = e.pageY;
     top = $(".small img").offset().top;
     left = $(".small img").offset().left;
     width = $(".small img").width();
     height = $(".small img").height();
     //
     imgWidth = $(".big img").width();
     imgHeight = $(".big img").height();
     rateX = (left+width-x)/width;
     rateY = (top+height-y)/height;
     if(rateX>0&&rateY>0&&rateX<=1&&rateY<=1){
      $(".big img").css("left",(rateX-0.5)*50+"%");
      $(".big img").css("top",(rateY-0.5)*50+"%");
     }
    })
   })
  </script>
 </body>
</html>