大家经常逛淘宝、天猫、京东这类网站的时候往往会看到一些图片展示的效果，例如：把鼠标放在图片上右侧会出现一个放大的预览区域，这就是所谓放大镜效果。今天闲着没事干，就打算复习一下JavaScript基础，用一下基础知识制作一个类似于淘宝的放大镜效果。
先说一下这个效果需要用到的一些基础知识：
css相对定位：position：absolute；
鼠标移入移出以及移动事件：onmouseover、onmouseout、onmousemove，记住这些事件一般不会单个出现
获取鼠标点击坐标：X轴：clientX，Y轴：clientY
当前元素相对于父元素的左位移：offsetLeft
当前元素相对于父元素的上位移：offsetTop
当前元素的实际高、宽度（不包括滚动条）：offsetWidth、offsetHeight
球当前元素的最小值，最大值：Math.min()、Math.max()；
话不多说直接上代码吧！
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>放大镜效果</title>
<style type="text/css">
*{
padding: 0;
margin: 0;
}
#demo{
display: block;
width: 400px;
height: 255px;
margin: 50px;
position: relative;
border: 1px solid #ccc;
}
#float-box{
position: relative;
z-index: 1;
}
#small-box{
display: none;
width: 160px;
height: 120px;
position: absolute;
background: #ffffcc;
border: 1px solid #ccc;
filter: alpha(opacity=50);
opacity: 0.5;
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>
</head>
<body>
<div id="demo">
<div id="float-box">
<div id="small-box"></div>
<img src="../images/macbook-small.jpg">
</div>
<div id="big-box">
<img src="../images/macbook-big.jpg">
</div>
</div>
<script type="text/javascript">
window.onload = function(){
//获取到需要的元素
var demo = document.getElementById('demo');
var smallBbox = document.getElementById('small-box');
var floatBox = document.getElementById('float-box');
var bigBox = document.getElementById('big-box');
var bigBoxImg = bigBox.getElementsByTagName('img')[0];
floatBox.onmouseover = function(){
smallBbox.style.display = "block";
bigBox.style.display = "block";
}
floatBox.onmouseout = function(){
smallBbox.style.display = "none";
bigBox.style.display = "none";
}
floatBox.onmousemove = function(e){
var _event = e || event;
console.log(_event.clientY);
var l = _event.clientX - demo.offsetLeft - floatBox.offsetLeft - smallBbox.offsetWidth/2;//除2是因为让鼠标点出现在放大遮罩的中心位置
var t = _event.clientY - demo.offsetTop - floatBox.offsetTop - smallBbox.offsetHeight/2;
var demoWidth = demo.offsetWidth;
var demoHeight = demo.offsetHeight;
var smallBboxWidth = smallBbox.offsetWidth;
var smallBboxHeight = smallBbox.offsetHeight;
//鼠标可以移动的最大XY的距离
var maxX = demoWidth - smallBboxWidth;
var maxY = demoHeight - smallBboxHeight;
l = Math.min(maxX,Math.max(0,l));
t = Math.min(maxY,Math.max(0,t));
smallBbox.style.left = l +"px";
smallBbox.style.top = t +"px";
var percentX = l / (floatBox.offsetWidth - smallBboxWidth);//求出小图遮罩的坐标占可移动区域的比例
var percentY = t / (floatBox.offsetHeight - smallBboxHeight);
bigBoxImg.style.left = -percentX *(bigBoxImg.offsetWidth - bigBox.offsetWidth) +"px";//大图对的移动方向和小图遮罩的移动方向相反
bigBoxImg.style.top = -percentY*(bigBoxImg.offsetHeight - bigBox.offsetHeight)+"px";
}
}
</script>
</body>
</html>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
