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JS放大镜特效（兼容版）

作者：互联网

原文链接：http://www.cnblogs.com/EvanLiu/p/4217563.html

原理

1.鼠标在小图片上移动时，通过捕获鼠标在小图片上的位置，定位大图片的相应位置

设计

1.页面元素：小图片、大图片、放大镜

2.技术点：事件捕获、定位

1）onmouseover：会在鼠标指针移动到指定的对象上时发生

2）onmouseout：会在鼠标指针移出指定的对象时发生

3）onmousemove：会在鼠标指针移动时发生

4）各边距表示

5）ofgsetLeft与style.left对比

style.left返回的是字符串，比如：30px，offsetLeft返回的是数值30

style.left是可读写的，offsetLeft是只读写的，所以该改变div的位置，只能修改style.left

style.left的值需事件定义，否则取到的值为空

3.难点：计算

objMark.onmousemove = function (ev) {
　　var _event = ev || window.event;  //兼容多个浏览器的event参数模式

   var left = _event.clientX - objDemo.offsetLeft - objSmallBox.offsetLeft - objFloatBox.offsetWidth / 2;
   var top = _event.clientY - objDemo.offsetTop - objSmallBox.offsetTop - objFloatBox.offsetHeight / 2;
　　//当放大镜出超出横向范围的时候
   if (left < 0) {
       left = 0;
   } else if (left > (objMark.offsetWidth - objFloatBox.offsetWidth)) {
       left = objMark.offsetWidth - objFloatBox.offsetWidth;
   }
　　//当放大镜查出纵向范围的时候
   if (top < 0) {
        top = 0;
   } else if (top > (objMark.offsetHeight - objFloatBox.offsetHeight)) {
        top = objMark.offsetHeight - objFloatBox.offsetHeight;

   }

   objFloatBox.style.left = left + "px";   //oSmall.offsetLeft的值是相对什么而言
   objFloatBox.style.top = top + "px";

   var percentX = left / (objMark.offsetWidth - objFloatBox.offsetWidth);
   var percentY = top / (objMark.offsetHeight - objFloatBox.offsetHeight);

   objBigBoxImage.style.left = -percentX * (objBigBoxImage.offsetWidth - objBigBox.offsetWidth) + "px";
   objBigBoxImage.style.top = -percentY * (objBigBoxImage.offsetHeight - objBigBox.offsetHeight) + "px";
}

 

源码

<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <title>放大镜</title>
    <style>
        * {
            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>

        //页面加载完毕后执行
        window.onload = function () {

            var objDemo = document.getElementById("demo");
            var objSmallBox = document.getElementById("small-box");
            var objMark = document.getElementById("mark");
            var objFloatBox = document.getElementById("float-box");
            var objBigBox = document.getElementById("big-box");
            var objBigBoxImage = objBigBox.getElementsByTagName("img")[0];

            objMark.onmouseover = function () {
                objFloatBox.style.display = "block"
                objBigBox.style.display = "block"
            }

            objMark.onmouseout = function () {
                objFloatBox.style.display = "none"
                objBigBox.style.display = "none"
            }

            objMark.onmousemove = function (ev) {

                var _event = ev || window.event;  //兼容多个浏览器的event参数模式

                var left = _event.clientX - objDemo.offsetLeft - objSmallBox.offsetLeft - objFloatBox.offsetWidth / 2;
                var top = _event.clientY - objDemo.offsetTop - objSmallBox.offsetTop - objFloatBox.offsetHeight / 2;

                if (left < 0) {
                    left = 0;
                } else if (left > (objMark.offsetWidth - objFloatBox.offsetWidth)) {
                    left = objMark.offsetWidth - objFloatBox.offsetWidth;
                }

                if (top < 0) {
                    top = 0;
                } else if (top > (objMark.offsetHeight - objFloatBox.offsetHeight)) {
                    top = objMark.offsetHeight - objFloatBox.offsetHeight;

                }

                objFloatBox.style.left = left + "px";   //oSmall.offsetLeft的值是相对什么而言
                objFloatBox.style.top = top + "px";

                var percentX = left / (objMark.offsetWidth - objFloatBox.offsetWidth);
                var percentY = top / (objMark.offsetHeight - objFloatBox.offsetHeight);

                objBigBoxImage.style.left = -percentX * (objBigBoxImage.offsetWidth - objBigBox.offsetWidth) + "px";
                objBigBoxImage.style.top = -percentY * (objBigBoxImage.offsetHeight - objBigBox.offsetHeight) + "px";
            }
        }
    </script>
</head>
<body>
<div id="demo">
    <div id="small-box">
        <div id="mark"></div>
        <div id="float-box"></div>
        <img src="macbook-small.jpg"/>
    </div>
    <div id="big-box">
        <img src="macbook-big.jpg"/>
    </div>
</div>
</body>
</html>

效果：

 

转载于:https://www.cnblogs.com/EvanLiu/p/4217563.html

标签：style,放大镜,top,objFloatBox,兼容,offsetHeight,JS,offsetWidth,left
来源： https://blog.csdn.net/weixin_30295091/article/details/97127711