本文實例為大家介紹了基於javascript實現放大鏡效果的原理和程式碼，分享給大家供大家參考，具體內容如下：
原理：
A:放大鏡 B：小圖片
C：大圖片可視區域
D：大圖
滑鼠的位置應該在放大鏡的中央，所以滑鼠位置為：
clientX=A.offsetLeft()+B.offsetLeft+1/2*A.offsetWidth;
clientY=A.offsetTop()+B.offsetTop+1/2*A.offsetHeight;
滑鼠移動過程中:放大鏡A和大圖D是一起隨滑鼠成比例運動的，因為當放大鏡A的右邊框移動到與小圖B的右邊框重合時，大圖D也應該移動到了右邊框與C的右邊框重合的地方，所以，他們的移動比例是：(D.offsetWidth-C.offsetWidth)/(B.offsetWidth-A.offsetWidth)=b/a
HTML部分：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>放大镜效果</title>
<style>
*{
margin:0;
padding:0;
}
#demo{
position: relative;
margin:30px 50px;
width: 1000px;
height: 600px;
border: 1px solid #000;
}
#zhezhao{
position: absolute;
z-index:2;
background:red;
width:402px;
height:402px;
left: 20px;
top:20px;
opacity: 0;
}
#small{
position: absolute;
width:402px;
height:402px;
left: 20px;
top:20px;
border: 1px solid #000;
z-index: 1;
}
#small img{
position: absolute;
}
#big{
position: relative;
top: 20px;
left: 460px;
width:500px;
height:500px;
border: 1px solid #000;
overflow: hidden;
display: none;
z-index: 1;
}
#big img{
position: absolute;
}
#glass{
position: absolute;
width:100px;
height: 100px;
opacity: 0.3;
background:orange;
display: none;
}
</style>
</head>
<body>
<div id='demo'>
<div id='zhezhao'> </div>
<!-- 在ie浏览器中，当鼠标在放大镜上是，浏览器并不认为鼠标同样在小图的div上，所以加个遮罩层 兼容ie-->
<div id='small'>
<img src='images/small.png' alt=''>
<div id='glass'></div>
</div>
<div id='big'>
<img src='images/big.jpg' alt='' >
</div>
</div>
</body>
</html>
js部分：
<script>
window.onload=function(){
var demo =document.getElementById('demo');
var small =document.getElementById('small');
var big =document.getElementById('big');
var glass =document.getElementById('glass')
var image =document.getElementById('big').getElementsByTagName('img')[0];
var zhezhao=document.getElementById('zhezhao');
zhezhao.onmouseover=function(){
glass.style.display='block'
big.style.display='block'
}
zhezhao.onmouseout=function(){
glass.style.display='none'
big.style.display='none'
}
//弄清楚clientX，offsetLeft，left的关系，注意区分
zhezhao.onmousemove=function(ev){
var event=ev
var left=event.clientX-demo.offsetLeft-small.offsetLeft-glass.offsetWidth/2;
var top =event.clientY-demo.offsetTop -small.offsetTop -glass.offsetHeight/2;
if(left<0){
left=0;
}else if(left>(small.offsetWidth-glass.offsetWidth)){
left=small.offsetWidth-glass.offsetWidth
}
if(top<0){
top=0;
}else if(top>(small.offsetHeight- glass.offsetHeight)){
top=small.offsetHeight- glass.offsetHeight
}
glass.style.left =left+'px';
glass.style.top =top+'px';
var percent=(image.offsetWidth-big.offsetWidth)/(small.offsetWidth-glass.offsetWidth)
image.style.left=-percent*left+'px'
image.style.top =-percent*top+'px'
}
}
</script>
以上就是本文的全部內容，希望對大家實現javascript放大鏡效果有所幫助。
