首先是HTML：
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">2
<html xmlns="http://www.w3.org/1999/xhtml">3
<head>4
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />5
<title>按比例自动缩放图片</title>6
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<script type="text/javascript" src="js/jquery.js"></script>8
<script type="text/javascript" src="js/drawImg"></script>9
</head>10
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<body>12
<div id="imgBox" style="500px; height:400px; background:#cccccc; overflow:hidden">13
<img id="img1" alt="" src="images/1.jpg" onload="DrawImg(500,400);" />14
</div>15
</body>16
</html>再是JavaScript：
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function DrawImg(boxWidth,boxHeight)2
{
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var imgWidth=$("#img1").width();4
var imgHeight=$("#img1").height();5
//比较imgBox的长宽比与img的长宽比大小6
if((boxWidth/boxHeight)>=(imgWidth/imgHeight))7
{
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//重新设置img的width和height9
$("#img1").width((boxHeight*imgWidth)/imgHeight);10
$("#img1").height(boxHeight);11
//让图片居中显示12
var margin=(boxWidth-$("#img1").width())/2;13
$("#img1").css("margin-left",margin);14
}15
else16
{17
//重新设置img的width和height18
$("#img1").width(boxWidth);19
$("#img1").height((boxWidth*imgHeight)/imgWidth);20
//让图片居中显示21
var margin=(boxHeight-$("#img1").height())/2;22
$("#img1").css("margin-top",margin);23
}24
}25