js实现放大镜效果

成品效果展示如下 js实现放大镜效果
代码展示：
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>纯js制作放大镜效果</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        #box{
            width: 350px;
            height: 350px;
            margin-left:100px;
            margin-top:100px;
            border: 1px solid #000;;
            position:relative;
        }
        #small{
            width: 350px;
            height: 350px;
        }
        #big{
            position:absolute;
            width: 400px;
            height: 400px;
            border: 1px solid #000;
            right:-410px;
            top:0;
            overflow:hidden;
            display: none;
        }
        #mask{
            position:absolute;
            width: 175px;
            height: 175px;
            background-color: yellow;
            opacity:0.4;
            top:0;
            left:0;
            display: none;
        }
    </style>
</head>
<body>
<div id="box">
    <div id="small">
        <img src="images/001.jpg" alt="">
        <div id="mask"></div>
    </div>
    <div id="big">
        <img src="images/0001.jpg" alt="">
    </div>
</div>
<script>
    var box=document.getElementById("box");
    var small=document.getElementById("small");
    var big=document.getElementById("big");
    var smallimg=small.firstElementChild || firstChild;
    var bigimg=big.firstElementChild || firstChild;
    var mask=document.getElementById("mask");


    //鼠标移入移出显示隐藏事件
    small.onmouseenter=function(){
        mask.style.display="block"
        big.style.display="block"
    };
    //鼠标移出事件
    small.onmouseleave=function(){
        mask.style.display = "none"
        big.style.display = "none"
    };


    //鼠标在盒子中的位置
    small.onmousemove=function(event){
        event = event || window.event;
        //获取鼠标在盒子中的位置
        var mousex=getEventPageXY(event).pageX-box.offsetLeft;
        var mousey=getEventPageXY(event).pageY-box.offsetTop;

        //鼠标在盒子中移动的距离
        var movex=mousex-(mask.offsetWidth/2);
        var movey=mousey-(mask.offsetHeight/2);

        if(movex<=0){
            movex = 0
        }
        if(movex>=(box.offsetWidth-mask.offsetWidth)){
            movex = box.offsetWidth-mask.offsetWidth
        }
        if(movey<=0){
            movey = 0
        }
        if(movey>=(box.offsetHeight-mask.offsetHeight)){
            movey = box.offsetHeight-mask.offsetHeight;
        }
        mask.style.left = movex+"px";
        mask.style.top=movey+"px";

        //判断比例
        //小图片/大图片=小盒子移动的距离/大图片移动的距离
        var  bili=smallimg.offsetWidth/bigimg.offsetWidth;
        var  bigx=movex/bili;
        var  bigy=movey/bili;
        //取整
        bigx=Math.floor(bigx);
        bigy = Math.floor(bigy);

        //移动大图片
        bigimg.style.marginLeft=-bigx+"px";
        bigimg.style.marginTop=-bigy+"px";
    };
    //获取event对象的pageXY的兼容性封装
    function getEventPageXY(event){
        return{
            pageX:event.pageX || scroll().left+event.clientX,
            pageY:event.pageY || scroll().top+event.clientY
        }
    }
    //被卷去的头部和左边部分的兼容性封装
    function scroll(){
        if(window.pageXOffset!==undefined){
            return{
                left:window.pageXOffset,
                top:window.pageYOffset
            }
        }else{
            return{
                left:document.documentElement.scrollLeft,
                top:document.documentElement.scrollTop
            }
        }
    }
</script>
</body>
</html>
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js实现放大镜效果

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