js代码实现放大镜效果

每当打开淘宝,天猫等pc端时,看到心仪的物品时,点击图片时,便呈现出放大的效果。在没有去理解分析它的原理时,感觉非常的神奇,当真正地去接触,也是非常好理解。如下图展示所见:

 

很是常见,在此记载一下,毕竟好记性不如烂笔头。 

主要事件:

  • onmouseout
  • onmouseover
  • onmousemove

这种实现也是比较简单的,代码如下所示:

  1 <!doctype html>
  2 <html>
  3 <head>
  4     <meta charset="UTF-8">
  5     <title>放大镜</title>
  6     <style>
  7         * {
  8             margin: 0;
  9             padding: 0
 10         }
 11 
 12         #demo {
 13             display: block;
 14             width: 400px;
 15             height: 255px;
 16             margin: 50px;
 17             position: relative;
 18             border: 1px solid #ccc;
 19         }
 20 
 21         #small-box {
 22             position: relative;
 23             z-index: 1;
 24         }
 25 
 26         #float-box {
 27             display: none;
 28             width: 160px;
 29             height: 120px;
 30             position: absolute;
 31             background: #ffffcc;
 32             border: 1px solid #ccc;
 33             filter: alpha(opacity=50);
 34             opacity: 0.5;
 35         }
 36 
 37         #mark {
 38             position: absolute;
 39             display: block;
 40             width: 400px;
 41             height: 255px;
 42             background-color: #fff;
 43             filter: alpha(opacity=0);
 44             opacity: 0;
 45             z-index: 10;
 46         }
 47 
 48         #big-box {
 49             display: none;
 50             position: absolute;
 51             top: 0;
 52             left: 460px;
 53             width: 400px;
 54             height: 300px;
 55             overflow: hidden;
 56             border: 1px solid #ccc;
 57             z-index: 1;;
 58         }
 59 
 60         #big-box img {
 61             position: absolute;
 62             z-index: 5
 63         }
 64     </style>
 65     <script>
 66 
 67         //页面加载完毕后执行
 68         window.onload = function () {
 69 
 70             var objDemo = document.getElementById("demo");
 71             var objSmallBox = document.getElementById("small-box");
 72             var objMark = document.getElementById("mark");
 73             var objFloatBox = document.getElementById("float-box");
 74             var objBigBox = document.getElementById("big-box");
 75             var objBigBoxImage = objBigBox.getElementsByTagName("img")[0];
 76 
 77             objMark.onmouseover = function () {
 78                 objFloatBox.style.display = "block"
 79                 objBigBox.style.display = "block"
 80             }
 81 
 82             objMark.onmouseout = function () {
 83                 objFloatBox.style.display = "none"
 84                 objBigBox.style.display = "none"
 85             }
 86 
 87             objMark.onmousemove = function (ev) {
 88 
 89                 var _event = ev || window.event;  //兼容多个浏览器的event参数模式
 90 
 91                 var left = _event.clientX - objDemo.offsetLeft - objSmallBox.offsetLeft - objFloatBox.offsetWidth / 2;
 92                 var top = _event.clientY - objDemo.offsetTop - objSmallBox.offsetTop - objFloatBox.offsetHeight / 2;
 93 
 94                 //设置边界处理,防止移出小图片
 95                 if (left < 0) {
 96                     left = 0;
 97                 } else if (left > (objMark.offsetWidth - objFloatBox.offsetWidth)) {
 98                     left = objMark.offsetWidth - objFloatBox.offsetWidth;
 99                 }
100 
101                 if (top < 0) {
102                     top = 0;
103                 } else if (top > (objMark.offsetHeight - objFloatBox.offsetHeight)) {
104                     top = objMark.offsetHeight - objFloatBox.offsetHeight;
105 
106                 }
107 
108                 objFloatBox.style.left = left + "px";   //oSmall.offsetLeft的值是相对什么而言
109                 objFloatBox.style.top = top + "px";
110                 
111                 //求其比值
112                 var percentX = left / (objMark.offsetWidth - objFloatBox.offsetWidth);
113                 var percentY = top / (objMark.offsetHeight - objFloatBox.offsetHeight);
114                 
115                 //方向相反,小图片鼠标移动方向与大图片相反,故而是负值
116                 objBigBoxImage.style.left = -percentX * (objBigBoxImage.offsetWidth - objBigBox.offsetWidth) + "px";
117                 objBigBoxImage.style.top = -percentY * (objBigBoxImage.offsetHeight - objBigBox.offsetHeight) + "px";
118             }
119         }
120     </script>
121 </head>
122 <body>
123     <div id="demo">
124         <div id="small-box">
125             <div id="mark"></div>
126             <div id="float-box"></div>
127             <img src="img/macbook-small.jpg"/>
128         </div>
129         <div id="big-box">
130             <img src="img/macbook-big.jpg"/>
131         </div>
132     </div>
133 </body>
134 </html>

这里面需要区别的是offsetLeft和style.left:

offsetLeft 获取的是相对于父对象的左边距;left 获取或设置相对于 具有定位属性(position定义为relative)的父对象 的左边距;

  • offsetLeft返回的数值,而style.left则返回的是字符串;
  • offsetLeft是只读的,style.left可读写的;
  • style.left的值需要事先定义,否则取到的值为空,而且必须要定义在html里,如果写在样式里面,是取不出它的值的

这是这个代码的要点之一,另外一个就是去要计算其比例。根据对应比例,进行代码的显示。

另外,小图片和大图片的显示,移动方向是相反的,所以比例前面会乘以一个负号。这个需要注意。

posted @ 2017-03-23 12:07  Seraphjin  阅读(19034)  评论(1编辑  收藏  举报