图片上传前预览的写法

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
 
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>By：DragonDean</title>
        <script type="text/javascript">
            //下面用于图片上传预览功能
            function setImagePreview(avalue) {
                var docObj = document.getElementById("doc");
 
                var imgObjPreview = document.getElementById("preview");
                if(docObj.files && docObj.files[0]) {
                    //火狐下，直接设img属性
                    imgObjPreview.style.display = 'block';
                    imgObjPreview.style.width = '150px';
                    imgObjPreview.style.height = '180px';
                    //imgObjPreview.src = docObj.files[0].getAsDataURL();
 
                    //火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式
                    imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
                } else {
                    //IE下，使用滤镜
                    docObj.select();
                    var imgSrc = document.selection.createRange().text;
                    var localImagId = document.getElementById("localImag");
                    //必须设置初始大小
                    localImagId.style.width = "150px";
                    localImagId.style.height = "180px";
                    //图片异常的捕捉，防止用户修改后缀来伪造图片
                    try {
                        localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
                        localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
                    } catch(e) {
                        alert("您上传的图片格式不正确，请重新选择!");
                        return false;
                    }
                    imgObjPreview.style.display = 'none';
                    document.selection.empty();
                }
                return true;
            }
        </script>
    </head>
 
    <body>
        <table width="100%" border="0" cellspacing="0" cellpadding="0">
            <tbody>
                <tr>
                    <td height="101" align="center">
                        <div id="localImag"><img id="preview" src="http://blog.chuangling.net/Public/images/top.jpg" width="150" height="180" style="display: block; width: 150px; height: 180px;"></div>
                    </td>
                </tr>
                <tr>
                    <td align="center" style="padding-top:10px;"><input type="file" name="file" id="doc" style="width:150px;" onchange="javascript:setImagePreview();"></td>
                </tr>
            </tbody>
        </table>
    </body>
 
</html>