JavaScript 实现 PC 端商品放大镜特效

<!DOCTYPE html>
<html>

<head>
 <meta charset="UTF-8">
 <title></title>
 <style type="text/css">
  * {
   margin: 0px;
   padding: 0px;
  }
  
  #min {
   width: 350px;
   height: 350px;
   border: 1px solid #ccc;
   position: absolute;
   left: 50px;
   top: 50px;
  }
  
  #min img {
   width: 350px;
   height: 350px;
  }
  
  #max {
   width: 500px;
   height: 500px;
   position: absolute;
   left: 500px;
   top: 50px;
   border: 1px solid #ccc;
   overflow: hidden;
   display: none;
  }
  
  #max img {
   position: absolute;
   left: 0;
   top: 0;
  }
  
  #mask {
   width: 200px;
   height: 200px;
   background: rgba(255, 0, 0, 0.5);
   position: absolute;
   left: 0px;
   top: 0px;
   cursor: pointer;
   display: none;
  }
 </style>
</head>

<body>
 <div id="min">
  <img src="img/min.jpg" alt="" />
  <div id="mask"></div>
 </div>
 <div id="max">
  <img src="img/max.jpg" id="maxImg" />
 </div>
 <script type="text/javascript">
  // 1.鼠标经过小盒子，遮罩层出现，大盒子出现
  // 2.遮罩层跟随鼠标移动
  // 3.遮罩层移动，大盒子里的图片反方向移动
  var oMin = document.getElementById('min');
  var oMax = document.getElementById('max');
  var oMask = document.getElementById('mask');
  var oMaxImg = document.getElementById('maxImg');
  oMin.onmousemove = function(e) {
   // 1.鼠标经过小盒子，遮罩层和大盒子出现
   oMask.style.display = 'block';
   oMax.style.display = 'block';
   // 2.拿到鼠标在小盒子上的坐标
   var minX = e.clientX - oMin.offsetLeft;
   var minY = e.clientY - oMin.offsetTop;
   // 3.将鼠标放置在遮罩层的中间
   minX = minX - oMask.offsetWidth / 2;
   minY = minY - oMask.offsetHeight / 2;
   // 4.遮罩层可以移动的最大距离
   var maxWidth = oMin.offsetWidth - oMask.offsetWidth;
   var maxHeight = oMin.offsetHeight - oMask.offsetHeight;
   // 限定遮罩层的位置
   if (minX > maxWidth) {
    minX = maxWidth;
   } else if (minX <= 0) {
    minX = 0;
   }
   if (minY > maxHeight) {
    minY = maxHeight;
   } else if (minY <= 0) {
    minY = 0;
   }
   // 设定遮罩层的偏移
   oMask.style.left = minX + 'px';
   oMask.style.top = minY + 'px';
   // 大图片移动的距离=遮罩层移动的距离/遮罩层可以移动的最大距离*大图片最大移动距离
   var ratioX = minX / maxWidth;
   var ratioY = minY / maxHeight;
   // 计算出大图片的移动距离
   oMaxImg.style.left = -ratioX * (oMaxImg.offsetWidth - oMax.offsetWidth) + 'px';
   oMaxImg.style.top = -ratioY * (oMaxImg.offsetHeight - oMax.offsetHeight) + 'px';
  };
  // 鼠标移开，遮罩层和大盒子消失
  oMin.onmouseout = function() {
   oMask.style.display = 'none';
   oMax.style.display = 'none';
  }
 </script>
</body>

</html>