javascript上传前图片预览代码

</head>

<script language="javascript" type="text/javascript">
 function PreviewImg(imgFile)
{
    var newPreview = document.getElementById("newPreview");
    newPreview.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgFile.value;
    newPreview.style.width = "158px";
    newPreview.style.height = "180px";
}
</script>

<div id="newPreview"></div>

<asp:FileUpload ID="FileUpload1" onchange="PreviewImg(this)" runat="server"   Width="408px" />
 

o.style.visibility = "visible";
width_img=o.offsetWidth;
height_img=o.offsetHeight;

var width=274;   //预定义宽
var height=100;  //预定义高

var ratW;        //宽的缩小比例
var ratH;        //高的缩小比例
var rat;         //实际使用的缩小比例
if(width_img<width && height_img<height)
{
    //如果比预定义的宽高小，原图显示。
    o.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod = "image";
    return;

   
}else{
    //如果大的化，要把 sizingMethod改成scale 如果属性是image,不管怎么改div的宽高，都不起作用
    o.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod = "scale";

}
ratH=height/height_img;
ratW=width/width_img;
if(ratH<ratW)       //选择最小的作为实际的缩小比例
    rat=ratH;
else
    rat=ratW;
   
width_img=width_img * rat;
height_img=height_img * rat;
o.style.width=width_img;
o.style.height=height_img;
}修改ShowImage方法 function ShowImage(path){
 //处理前是原图，先将其隐藏，
 document.all.divShow.style.visibility = "hidden";
document.all.divShow.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = path;
  document.all.divShow.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod = "image";
//过一小会获取div的宽高.
setTimeout("setImg(document.all.divShow)",100);
}