在客户端用js动态预览图片的问题,好长时间了,还是没有解决,帮忙呀

再IE下应该是可用的：<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>
<head>
<title>Untitled</title>
</head>
<script language="JavaScript">
function trim(str) 
{
    regExp1 = /^ */;    
    regExp2 = / *$/;    
    return str.replace(regExp1,'').replace(regExp2,'');
}
var i=0;
function show(){
document.Form1.a.value=document.Form1.UploadFileBox.value;
//    document.Form1.UploadFileBox.value = trim(document.Form1.UploadFileBox.value);
    document.all.preview.src = document.Form1.UploadFileBox.value;     
    var showimg = new Image();
    showimg.src = document.Form1.UploadFileBox.value;
    if(showimg.width >= 400){
        var ori_w= showimg.width;
        var ori_h = showimg.height;
        showimg.width = 400;
        showimg.height = ori_h * showimg.width / ori_w;
    } else {
        if(showimg.height >= 400){
            var ori_w2= showimg.width;
            var ori_h2 = showimg.height;
            showimg.height = 400;
            showimg.width = ori_w2 * showimg.height / ori_h2;
        } else{
            showimg.height = showimg.height;
            showimg.width = showimg.width;
        }
    }
    document.all.preview.style.width = showimg.width;
    document.all.preview.style.height = showimg.height;
}
</script>
<body><form name="Form1" method="post" action="UploadImage.aspx?classid=1" id="Form1" enctype="multipart/form-data">
............
<input type="text" name ="a">
<TD><input name="UploadFileBox" id="UploadFileBox" type="file" style="WIDTH: 352px; HEIGHT: 22px" size="39" onpropertychange ="show()" ></TD>
............</form>
<img src="aaa.gif" id="preview" height="200" width=400></body>
</html>