JavaScript实现鼠标跟随小球动画

<!DOCTYPE html>
<html>
<head>
  <title>follow mouse</title>
</head>
<style type="text/css">
  *{
    margin: 0;
    padding:0;
  }
  #div1{width: 50px;height: 50px;background: red;color:#fff;text-align: center;line-height: 50px; position: absolute;transition: all 0.5s; }
  #div2{width: 50px;height: 50px;background: green;color:#fff;text-align: center;line-height: 50px;position:
  absolute;transition: all 0.5s; }

  .box1{
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;
  }
  .box2{
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;
    }
</style>

<body>
  <div class="box1" onmousemove="b1()">
    <div id="div1" >1</div>
  </div>
  <div class="box2" onmousemove="b2()">
    <div id="div2">2</div>
  </div>
</body>
<script type="text/javascript">
  function b1(ev) {
    var oEvent = ev || event;
    var oDiv = document.getElementById('div1');
    if( oEvent.clientX<350&&oEvent.clientY<350){
    oDiv.style.left = oEvent.clientX + 'px';
    oDiv.style.top = oEvent.clientY + 'px';
    }

  }
  function b2(ev){
    var oEvent=ev||event;
    var oDiv=document.getElementById('div2');
    if( oEvent.clientX<350&&oEvent.clientY<750){
      oDiv.style.left=oEvent.clientX+'px';
      oDiv.style.top=oEvent.clientY+'px';
    }
  }
</script>
</html>