实现局部放大图片功能

图片和具体代码也可以在我的github中找到，地址是https://github.com/Longweibing/TaobaoPicBigger

代码实现如下：

<!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;
            cursor: move;
        }


        #mark {
            position: absolute;
            display: block;
            width: 400px;
            height: 255px;
            z-index: 10;
            background: #fff;
            filter: alpha(opacity=0);
            opacity: 0;
            cursor: move;
        }


        #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) {
                //请补充此处鼠标移动时的响应方法
                var _event = ev;
                var left   = _event.clientX - objDemo.offsetLeft - objSmallBox.offsetLeft - objFloatBox.offsetWidth / 2;
                var top    = _event.clientY - objDemo.offsetTop - objSmallBox.offsetTop - objFloatBox.offsetHeight / 2;

                objFloatBox.style.left = left + "px";
                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";

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

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

            }
        }
    </script>
</head>
<body>
<div id="demo">
    <div id="small-box">
        <div id="mark"></div>
        <div id="float-box"></div>
        <img src="small_pic.jpg"/>
    </div>
    <div id="big-box">
        <img src="big_pic.jpg"/>
    </div>
</div>
</body>
</html>

效果图：