JavaScript实现简易放大镜最全代码解析（ES5）

本文实例为大家分享了JavaScript实现简易放大镜的具体代码，供大家参考，具体内容如下

完整代码：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>ES5放大镜</title>
    <style>
        .box {
            width: 170px;
            height: 180px;
            margin: 100px 200px;
            border: 1px solid #ccc;
            position: relative;
        }
        .small {
            position: relative;
        }
        .big {
            width: 300px;
            height: 320px;
            position: absolute;
            top: 30px;
            left: 220px;
            overflow: hidden;
            border: 1px solid #ccc;
            display: none;
        }
        .mask {
            width: 100px;
            height: 100px;
            background: rgba(255,255,0,0.3);
            position: absolute;
            top: 0;
            left: 0;
            cursor: move;
            display: none;
        }
        .big img{
            position: absolute;
            left: 0;
            top: 0;
        }
    </style>
</head>
<body>
    <div class="box" id="box">
        <div class="small">
            <img src="img/shirt_1.jpg" alt="picture"/>
            <div class="mask"></div>
        </div>
        <div class="big">
            <img src="img/shirt_1_big.jpg" alt="picture"/>
        </div>
    </div>
</body>
<script>
 var box = document.getElementById('box');
 var small = box.children[0];//放小图的盒子
 var big = box.children[1];//放大图的盒子
 var mask = small.children[1];//半透明鼠标移动跟随盒子
 var bigImage = big.children[0];//大图片
 small.onmouseover = function(event){
     big.style.display = 'block';
     mask.style.display = 'block';
 }
 small.onmouseout = function(){
     big.style.display = 'none';
     mask.style.display = 'none';
 }
 //移动事件，注意mask的定位相对的是samll
 small.onmousemove = function(event){
     var event = event || window.event;//事件对象
     // console.log(this.offsetLeft);//0,注意offsetLeft返回距离是一个带有定位的父级的左侧距离
     var x = event.clientX-this.offsetParent.offsetLeft-mask.offsetWidth/2;//此处不能用small的offsetLeft,用obj的offsetLeft
     var y = event.clientY-this.offsetParent.offsetTop-mask.offsetHeight/2;
     //限制半透明盒子出界
     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";
     //大图片放大
     bigImage.style.left = -x*big.offsetWidth/small.offsetWidth + 'px';
     bigImage.style.top = -y*big.offsetHeight/small.offsetHeight + 'px';
     //big.offsetWidth/small.offsetWidth是放大倍数
     //因为小图鼠标下移，大图上移，故用负数
 }
</script>
</html>

图片：

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