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javascript预览图片，按比例控制图片大小
<html ><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312" /><title>图片预览</title>
<script>
function PreviewPhotoatwidth(photo_file,img_object,imgwidth)
{
var fileext=photo_file.value.substring(photo_file.value.lastIndexOf("."),photo_file.value.length); fileext=fileext.toLowerCase(); if ((fileext!='.jpg')&&(fileext!='.gif')&&(fileext!='.jpeg')&&(fileext!='.png')&&(fileext!='.bmp')) {alert("对不起，系统仅支持标准格式的照片，请您调整格式后重新上传，谢谢 ！"); photo_file.focus();
} else { img_object.src=photo_file.value; if (img_object.width>imgwidth) { img_object.width=imgwidth; } }
}</script></head><body><table width="100%" border="0" cellspacing="0" cellpadding="0"> <tr> <td align="center"><img id="picpreview" alt='预览' /></td> </tr> <tr> <td align="center"><form id="form1" name="form1" enctype="multipart/form-data" method="post" action=""> <label>update <input type="file" id="uppic" name="uppic" onchange="javascript:PreviewPhotoatwidth(this,picpreview,260)" /> </label> </form> </td> </tr> <tr> <td> </td> </tr></table></body></html>从一个CNBLOGS朋友那里找到 记下 分享
http://www.cnblogs.com/cowboy/archive/2006/10/14/390808.html
