原生js实现放大镜特效

本文实例为大家分享了js实现放大镜特效的具体代码，供大家参考，具体内容如下

掌握页面元素定位和移动

放大镜关键原理：鼠标在小图片上移动时，通过捕捉鼠标在小图片上的位置定位大图片的相应位置

技术点：事件捕获、定位

offsetLeft与style.left的对比：
1）offsetLeft是与父级元素的距离，不包过滚动条的距离
2）style.left返回的是字符串，如30px，offsetLeft返回的是数值30
3）style.lft是可读写的，offsetLeft是只读的，所以要改变div的位置只能修改style.left
4）style.left的值需要事先定义，否则取到的值为空
难点：计算：如何让小图片的放大镜和大图片同步移动

距离定位图解：

具体代码：

<!DOCTYPE html>
<html>
<head lang="en">
 <meta charset="UTF-8">
 <title></title>
</head>
<style type="text/css">
 *{
 margin: 0;
 padding: 0;
 }
 #demo{
 display: block;
 width: 400px;
 height: 255px;
 margin: 50px;
 position: relative;
 border: 1px solid #ccc;
 }
 #small-box{
 position: relative;
 z-index: 1;
 }
 #float-box{
 display: none;
 width: 160px;
 height: 120px;
 position: absolute;
 background: #ffffcc;
 border: 1px solid #ccc;
 filter: alpha(opacity=50);
 opacity: 0.5;
 }
 #mark{
 position: absolute;
 display: block;
 width: 400px;
 height: 255px;
 background-color: #fff;
 filter: alpha(opacity=0);
 opacity: 0;
 z-index: 10;
 }
 #big-box{
 display: none;
 position: absolute;
 top: 0;
 left: 460px;
 width: 400px;
 height: 300px;
 overflow: hidden;
 border: 1px solid #ccc;
 z-index: 1;
 }
 #big-box img{
 position: absolute;
 z-index: 5;
 }
</style>
<script>
 window.onload=function(){
 var $=function(id){
  return document.getElementById(id);
 }
 var Demo = $("demo");
 var SmallBox = $("small-box");
 var Mark = $("mark");
 var FloatBox = $("float-box");
 var BigBox = $("big-box");
 var BigBoxImage = BigBox.getElementsByTagName("img")[0];
 Mark.onmouseover = function(){
  FloatBox.style.display = "block";
  BigBox.style.display = "block";
 }
 Mark.onmouseout = function(){
  FloatBox.style.display = "none";
  BigBox.style.display = "none";
 }
 Mark.onmousemove = function(e){
  var _event = e||window.event//兼容多个浏览器的参数模式
  var left = _event.clientX - Demo.offsetLeft - SmallBox.offsetLeft - FloatBox.offsetWidth/2;
  var top = _event.clientY - Demo.offsetTop - SmallBox.offsetTop - FloatBox.offsetHeight/2;
  if(left < 0){
  left = 0;
  }else if(left > Mark.offsetWidth - FloatBox.offsetWidth){
  left = Mark.offsetWidth - FloatBox.offsetWidth;
  }
  if(top < 0){
  top = 0;
  }else if(top > Mark.offsetHeight - FloatBox.offsetHeight){
  top = Mark.offsetHeight - FloatBox.offsetHeight;
  }
  FloatBox.style.left = left + 'px';
  FloatBox.style.top = top + 'px';
  var percentX = left / (Mark.offsetWidth - FloatBox.offsetWidth);
  var percentY = top / (Mark.offsetHeight - FloatBox.offsetHeight);
  BigBoxImage.style.left = -percentX * (BigBoxImage.offsetWidth - BigBox.offsetWidth)+'px';
  BigBoxImage.style.top = -percentY * (BigBoxImage.offsetHeight - BigBox.offsetHeight)+'px';
 }
 }
</script>
<body>
<div id="demo">
 <div id="small-box">
 <div id="mark"></div>
 <div id="float-box"></div>
 <img src="img/macbook-small.jpg" />
 </div>
 <div id="big-box">
 <img src="img/macbook-big.jpg" />
 </div>
</div>
</body>
</html>

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