原生JS实现简单放大镜效果

来源：酷升汽车网
本文实例为大家分享了原生JS实现放大镜效果的具体代码，供大家参考，具体内容如下
<html>
 
 <head>
 <meta charset="UTF-8">
 <title></title>
 <style type="text/css">
 * {
 margin: 0;
 padding: 0;
 }
 img{
 vertical-align: top;
 }
 .fdj {
 width: 350px;
 height: 350px;
 position: relative;
 margin: 100px auto;
 border: 1px solid gainsboro;
 }
 .small {
 position: relative;
 }
 .small img {
 width: 350px;
 }
 .mask {
 width: 100px;
 height: 100px;
 background: rgba(255, 255, 0, 0.4);
 position: absolute;
 left: 0;
 top: 0;
 cursor: move;
 display: none;
 }
 .big {
 position: absolute;
 top: 0;
 left: 360px;
 width: 500px;
 height: 500px;
 border: 1px solid gainsboro;
 overflow: hidden;
 display: none;
 }
 .big img{
 position: absolute;
 left: 0;
 top: 0;
 }
 </style>
 </head>
 
 <body>
 <div class="fdj">
 <div class="small">
 <img src="http://cdn.attach.qdfuns.com/notes/pics/201702/08/162503mw0fawb5b02va22i.jpg" />
 <div class="mask"></div>
 </div>
 <div class="big">
 <img src="http://cdn.attach.qdfuns.com/notes/pics/201702/08/162503mw0fawb5b02va22i.jpg" />
 </div>
 </div>
 </body>
 <script type="text/javascript">
 var fdj = document.querySelector('.fdj') // 获得最大的盒子
 var small = document.querySelector('.small'); //获取小图片盒子
 var big = document.querySelector('.big'); //获取大图片盒子
 var bigs = big.children[0] //大图片 
 var smalls = small.children[0] //小图片
 var mask = small.children[1]; //遮罩
 
 //鼠标移入小图片盒子
 small.onmouseover = function() {
 //鼠标移入图片盒子将遮罩与大图片显示
 mask.style.display = 'block';
 big.style.display = ' block';
 };
 
 //鼠标移出小图片盒子
 small.onmouseout = function() {
 //鼠标移出小图片盒子将遮罩与大图片隐藏
 mask.style.display = 'none';
 big.style.display = 'none';
 };
 
 var x=0;
 var y=0;
 //鼠标在小图片上移动时
 small.onmousemove = function(ev) {
 var ev = event || window.event;
 //让鼠标在遮罩正中
 //鼠标X坐标与Y坐标
 x = ev.clientX -this.offsetParent.offsetLeft- mask.offsetWidth / 2 ; 
 y = ev.clientY -this.offsetParent.offsetTop- mask.offsetHeight / 2 ;
 //将遮罩在小图片盒子中
 
 if (x<0) {
 x=0;
 }else if(x>small.offsetWidth-mask.offsetWidth){
 x = small.offsetWidth-mask.offsetWidth;
 }
 
 if(y<0){
 y=0;
 }else if(y>small.offsetHeight-mask.offsetHeight){
 y= small.offsetHeight-mask.offsetHeight
 }
 mask.style.left = x + 'px';
 mask.style.top = y + 'px';
 
 //大图与小图的比例
 
 /*var scalX = bigs.offsetWidth/small.offsetWidth;
 var scalY = bigs.offsetHeight/small.offsetHeight;*/
 
 var scalX = x/(small.offsetWidth-mask.offsetWidth);
 var scalY = y/(small.offsetHeight-mask.offsetHeight);
 
 bigs.style.left = -(x*scalX)+'px';
 bigs.style.top = -(y*scalY)+'px';
 
 };
 
 </script>
 
</html>