本文实例讲述了原生JavaScript实现的简单放大镜效果。分享给大家供大家参考，具体如下：
原理： 其实所谓的放大就是准备两张一样的图片，除大小不一样。鼠标移动到不同位置，将会显示大图片对应的图片内容。
完整代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>放大镜效果</title>
</head>
<body>
<div id="wrap" style="position: relative;width: 900px;margin: 0 auto;text-align: center;">
<div id="smallImg" style="width: 400px;height: 400px; position: relative;z-index: 1;">
<img src="small.jpg" style="width: 400px;height: 400px;"/>
<span id="filter" style="width: 200px;height: 200px;background-color: blue;opacity: 0.1;position: absolute;top: 0;left: 0; z-index: 2;cursor: move;display: none;">
<span>
</div>
<div id="bigImg" style="width: 400px;height: 400px;overflow: hidden;position: absolute;right: 0px;top: 0;display: none;">
<img src="large.jpg" style="width: 800px;height:800px; position: absolute;left: 0;top: 0;">
</div>
</div>
<script type="text/javascript">
var filter = document.getElementById('filter');
var smallImg = document.getElementById('smallImg');
var bigImg = document.getElementById('bigImg');
var wrap = document.getElementById('wrap');
var largeImgs = bigImg.getElementsByTagName('img')[0];
smallImg.onmouseover = function(){
bigImg.style.display = "inline-block";
filter.style.display = "inline-block";
}
smallImg.onmousemove = function(event){
var event = event || window.event;
var mouseleft = event.clientX - wrap.offsetLeft;
var mousetop = event.clientY - wrap.offsetTop;
var left = mouseleft<smallImg.offsetWidth/4?0:mouseleft>smallImg.offsetWidth*3/4?smallImg.offsetWidth/2:(mouseleft - filter.offsetWidth/2);
var top = mousetop<smallImg.offsetHeight/4?0:mousetop>smallImg.offsetHeight*3/4?smallImg.offsetHeight/2:(mousetop - filter.offsetWidth/2);
filter.style.left = left + "px";
filter.style.top = top +"px";
largeImgs.style.left = "-" + left*bigImg.offsetWidth/smallImg.offsetWidth + "px";
largeImgs.style.top = "-" + top*bigImg.offsetHeight/smallImg.offsetHeight + "px";
}
smallImg.onmouseout = function(){
bigImg.style.display = "none";
filter.style.display = "none";
}
</script>
</body>
</html>
运行效果：
希望本文所述对大家JavaScript程序设计有所帮助。
