js版面向对象图片放大镜

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>放大镜特效</title>
</head>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
#main{
position: relative;
}
#main2{
position: relative;
}
.smallimg{
width:300px;
height: 300px;
position: absolute;
top: 50px;
left: 50px;
}
.mark{
width:100px;
height:100px;
position: absolute;
z-index: 100;
top: 0;
background:rgba(0,0,0,.6);
display: none;
cursor: move;
}
.bigimg{
position: absolute;
top:50px;
left:400px;
width:300px;
height: 300px;
overflow: hidden;
display: none;
}
.img1{
width:300px;
height:300px;
display: block;
}
.img2{
width: 900px;
height: 900px;
display: block;
}
</style>
<body>
<div id="main">
<div class="smallimg">
<img src="img/1.jpg" class="img1"/>
<div class="mark">

</div>
</div>
<div class="bigimg">
<img src="img/1.jpg" class="img2"/>
</div>
</div>

</body>
<script type="text/javascript">
function Show(id){
if(!document.getElementsByClassName){
document.getElementsByClassName = function(className, element){
var children = (element || document).getElementsByTagName('*');
var elements = new Array();
for (var i=0; i<children.length; i++){
var child = children[i];
var classNames = child.className.split(' ');
for (var j=0; j<classNames.length; j++){
if (classNames[j] == className){
elements.push(child);
break;
}
}
}
return elements;
};
}

var _this=this;
var main=document.getElementById(id);
this.smallimg=main.getElementsByClassName('smallimg')[0];
this.bigimg=main.getElementsByClassName('bigimg')[0];
this.mark=main.getElementsByClassName('mark')[0];
this.img2=main.getElementsByClassName("img2")[0];
this.smallimg.onmouseover=function(event){
_this.over(event);
}
this.smallimg.onmousemove=function(event){
_this.move(event);
}
this.smallimg.onmouseout=function(event){
_this.out(event);
}
}
Show.prototype.over=function(event){
var _this=this;
this.bigimg.style.display="block";
this.mark.style.display="block";
_this.show(event);
}
Show.prototype.move=function(event){
var _this=this;
this.bigimg.style.display="block";
this.mark.style.display="block";
_this.show(event);
}
Show.prototype.out=function(event){
this.bigimg.style.display="none";
this.mark.style.display="none";
}
Show.prototype.show=function(event){
var e=e||window.event;
this.L=e.clientX-this.smallimg.offsetLeft-this.mark.offsetWidth/2;
this.T=e.clientY-this.smallimg.offsetTop-this.mark.offsetHeight/2;
this.minL=0;
this.minT=0;
this.maxL=this.smallimg.offsetWidth-this.mark.offsetWidth;
this.maxT=this.smallimg.offsetHeight-this.mark.offsetHeight;
if(this.L<this.minL){
this.L=0;
}else if(this.L>this.maxL){
this.L=this.maxL;
}
if(this.T<this.minT){
this.T=0;
}else if(this.T>this.maxT){
this.T=this.maxT;
}
this.mark.style.left=this.L+'px';
this.mark.style.top=this.T+'px';
this.img2.style.marginLeft=this.L*-3+'px';
this.img2.style.marginTop=this.T*-3+'px';
}
//实现继承
/*function Show2(id){
Show.call(this,id);
}
for(var i in Show.prototype){
Show2.prototype[i]=Show.prototype[i];
}*/
window.onload=function(){
var show=new Show('main');
//var show2=new Show2('main2');
}
</script>
</html>