Jquery 上传图片预览

 <input type="file" name="doc" id="doc" onchange="javascript:setImagePreview();">
    <p>
        <div id="localImag">
            <img id="preview" width="-1" height="-1" style="diplay: none" /></div>
        <input type="button" id="shagnchuan" value="上传" onclick="alert(img.width);" />
    </p>
    <script type="text/javascript">
        function setImagePreview() {
            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 = 'auto';
                imgObjPreview.style.height = 'auto';
                //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 = "320";
                localImagId.style.height = "200";
                //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;
        }