调试易

        //检查插入是否为图片
        var img=null;
        function chkimg(inp)
        {
            img=document.getElementById("imgShow");
            img.src=inp;
            isimg();
        }
        function notimg()
        {
            document.getElementById("imgShow").src="../../property/property_img/default.jpg"
            document.getElementById("txtImageSize").value='noimage';
        }
        function isimg()
        {
            var noimage=document.getElementById("txtImageSize").value;
            noimage= img.offsetWidth +"x"+ img.offsetHeight;
        }
<asp:Image ID="imgShow" runat="server" Height="300px" Width="400px" AlternateText="Can't find a photo" onerror="notimg()" /><asp:FileUpload ID="myUlf" runat="server"/>
<asp:LinkButton ID="btnUp" runat="server" OnClientClick="chkimg(myUlf.value)" OnClick="btnUp_ServerClick">Upload</asp:LinkButton>为什么点了上传,显示了上传图片的尺寸后,又立马执行了notimg();