jquery实现图片放大镜效果

<div id="box">
    <div id="big">
      <div>
        <img src="./img/可达鸭.jpg" alt="">
      </div>
      <div id="fd"></div>
    </div>
    <div id="fdshow">
      <img src="./img/可达鸭.jpg" alt="">
    </div>
</div>

<style>
    *{
      margin: 0px;
      padding: 0px;
    }
    #box{
      position: relative;
    }
    #big{
      width: 500px;
      height: 300px;
    }
    #big img{
      width: 500px;
      height: 300px;
    }
    #fd{
      width: 100px;
      height: 100px;
      background-color: white;
      opacity: 0.4;
      position: absolute;
      top: 0;
      left: 0;
      display: none;
    }
    #fdshow{
      width: 200px;
      height: 200px;
      overflow: hidden;
      position: relative;
      border: 1px solid;
    }
    #fdshow>img{
      width: 1000px;
      height: 600px;
      position: absolute;
      top: 0px;
      left: 0px;
    }
</style>

<script>
    $("#big img").on("mousemove",function(a){
      var x=a.pageX-$("#big").offset().left;
      var y=a.pageY-$("#big").offset().top;
      console.log(x,y)
      var style1={
        top:y,               
        left:x,
        "display":"block"
      };
      $("#fd").css(style1);
      var style2={ 
        'left':-2*x,
  'top':-2*y
      };
      $("#fdshow>img").css(style2)
    })
</script>