本文实例为大家分享了js实现放大镜特效的具体代码，供大家参考，具体内容如下
掌握页面元素定位和移动
放大镜关键原理：鼠标在小图片上移动时，通过捕捉鼠标在小图片上的位置定位大图片的相应位置
技术点：事件捕获、定位
offsetLeft与style.left的对比：
1）offsetLeft是与父级元素的距离，不包过滚动条的距离
2）style.left返回的是字符串，如30px，offsetLeft返回的是数值30
3）style.lft是可读写的，offsetLeft是只读的，所以要改变div的位置只能修改style.left
4）style.left的值需要事先定义，否则取到的值为空
难点：计算：如何让小图片的放大镜和大图片同步移动
距离定位图解：
具体代码：
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<style type="text/css">
*{
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>
window.onload=function(){
var $=function(id){
return document.getElementById(id);
}
var Demo = $("demo");
var SmallBox = $("small-box");
var Mark = $("mark");
var FloatBox = $("float-box");
var BigBox = $("big-box");
var BigBoxImage = BigBox.getElementsByTagName("img")[0];
Mark.onmouseover = function(){
FloatBox.style.display = "block";
BigBox.style.display = "block";
}
Mark.onmouseout = function(){
FloatBox.style.display = "none";
BigBox.style.display = "none";
}
Mark.onmousemove = function(e){
var _event = e||window.event//兼容多个浏览器的参数模式
var left = _event.clientX - Demo.offsetLeft - SmallBox.offsetLeft - FloatBox.offsetWidth/2;
var top = _event.clientY - Demo.offsetTop - SmallBox.offsetTop - FloatBox.offsetHeight/2;
if(left < 0){
left = 0;
}else if(left > Mark.offsetWidth - FloatBox.offsetWidth){
left = Mark.offsetWidth - FloatBox.offsetWidth;
}
if(top < 0){
top = 0;
}else if(top > Mark.offsetHeight - FloatBox.offsetHeight){
top = Mark.offsetHeight - FloatBox.offsetHeight;
}
FloatBox.style.left = left + 'px';
FloatBox.style.top = top + 'px';
var percentX = left / (Mark.offsetWidth - FloatBox.offsetWidth);
var percentY = top / (Mark.offsetHeight - FloatBox.offsetHeight);
BigBoxImage.style.left = -percentX * (BigBoxImage.offsetWidth - BigBox.offsetWidth)+'px';
BigBoxImage.style.top = -percentY * (BigBoxImage.offsetHeight - BigBox.offsetHeight)+'px';
}
}
</script>
<body>
<div id="demo">
<div id="small-box">
<div id="mark"></div>
<div id="float-box"></div>
<img src="img/macbook-small.jpg" />
</div>
<div id="big-box">
<img src="img/macbook-big.jpg" />
</div>
</div>
</body>
</html>
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