javascript 上传图片前预览图片

<div id="localImag"><img  id="preview" width="-1" height="-1" style="display:none" /></div>
<asp:FileUpload ID="file_head" runat="server"  onchange="javascript:setImagePreview();" />

<script type="text/javascript">
    function setImagePreview() {
        var docObj = document.getElementById("ctl00_ContentMain_file_head");
        var fileName = docObj.value;
        if (!fileName.match(/.jpg|.gif|.png|.bmp/i)) {
            alert('您上传的图片格式不正确，请重新选择！');
            return false;
        }

        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 = '63px';
            imgObjPreview.style.height = '63px';
            //imgObjPreview.src = docObj.files[0].getAsDataURL();
            if (window.navigator.userAgent.indexOf("Chrome") >= 1 || window.navigator.userAgent.indexOf("Safari") >= 1) {
                imgObjPreview.src = window.webkitURL.createObjectURL(docObj.files[0]);
            }
            else {
                imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
            }
        } else {
            //IE下，使用滤镜
            docObj.select();
            docObj.blur();
            var imgSrc = document.selection.createRange().text;
            var localImagId = document.getElementById("localImag");
            //必须设置初始大小
            localImagId.style.width = "63px";
            localImagId.style.height = "63px"; 
            //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>

此js解决360浏览器显示图片问题。因为360浏览器6.2用的是Chrome的内核，而

window.URL.createObjectURL(docObj.files[0]);

只有在火狐下才认得到，chrome中不认识window.URL.createObjectURL，所有用Safari的window.webkitURL.createObjectURL