上传图片在客户端用Javascript做图片检验，并显示图片缩略图

        function PreviewImage(x)
        {
            
            //var x = document.getElementById('File1');
            var xid=x.id+"";
            var index=xid.substr(xid.length-1,1);
            
            if(!x || !x.value) 
                {                         
                return false;
                }
            var patn = /\.jpg$|\.jpeg$|\.bmp$|\.gif$/i;
            try
            {
                var obj = document.getElementById('PhotoPreviewImg'+index);
                
                var barType=index;
                //默认普通标题图
                var width=120;
                var height=80;
                
                if (barType==2) //首页标题图
                {
                    width=120;
                    height=90;
                }
                else if (barType==3) //焦点图
                {
                    width=320;
                    height=240;
                }
                if(patn.test(x.value))
                    {
                    var prvImg = "<img src='file://localhost/" + x.value + "' style='width: "+ width +"px; height: "+ height +"px; border: 1;' />";                    
                    var prvImgsrc = 'file://localhost/' + x.value;
                    document.getElementById("PhotoPreviewImg"+index).innerHTML=prvImg;
                    //setTimeout('CheckImg()',300);
                    //imgwh = new Image();
                    //imgwh.src = "file://localhost/" + x.value;
                    //CheckImg();
                    } 
                else
                    {                    
                    alert("您选择的似乎不是图像文件");
                    return false;
                    }
            
            }
            catch(e)
            {
             alert("您选择文件无法预览，或网络故障无法上传，请稍候再试！");
             return false;
            }
        }
        
    
         
 
    
        function CheckImg()
        {
            if(document.getElementById("PhotoPreviewImg").fileSize==-1||document.getElementById("PhotoPreviewImg").fileSize>5000000)
                        {
                             document.getElementById("File1").disabled=false;
                             //document.getElementById("PhotoPreviewImg").className='imgPrev0';
                             document.getElementById("PhotoPreviewImg").src="";
                             LoadEmptyImage ();
                             alert("您选择文件超过5M，无法上传！");

                             return false;                                
                        }
            else
            {
                document.getElementById("File1").disabled=false;
            }
                    
                document.getElementById("PhotoPreviewImg").className='';
                var originwidth=document.getElementById("PhotoPreviewImg").width*10;
                var originheight=document.getElementById("PhotoPreviewImg").height*10;
                var scale=originwidth/originheight;                        
                document.getElementById("PhotoPreviewImg").style.top=20;
                document.getElementById("PhotoPreviewImg").style.left=20;
                
                if(scale>0.8)
                    {
                    document.getElementById("PhotoPreviewImg").className='imgPrev2';
                    var largerheight=document.getElementById("PhotoPreviewImg").height;
                    var leftover=(150-largerheight)/2;
                    document.getElementById("PhotoPreviewImg").style.marginLeft=2;                
                    document.getElementById("PhotoPreviewImg").style.marginTop=leftover;
                    }
                else
                    {                                                            
                    document.getElementById("PhotoPreviewImg").style.marginTop=2;
                    document.getElementById("PhotoPreviewImg").className='imgPrev1';
                    var largerwidth=document.getElementById("PhotoPreviewImg").width;
                    var leftover=(120-largerwidth)/2;                        
                    document.getElementById("PhotoPreviewImg").style.marginLeft=leftover;
                    }                                                

                    return true;
    
        }

    <script type="text/javascript" defer>
            function checkit(obj)
            {
                if (obj.value.length >= 16)
                {
                    alert("在这里输入照片标题，不超过16个字！");
                    var str = obj.value;
                    obj.value = str.substring(0,16);
                    return false;
                }
                return true;
            }
            function empty()
            {
                if(document.getElementById("<%= phDescription1.ClientID%>").value == "" || document.getElementById("<%= phDescription1.ClientID%>").value == "在这里输入照片标题，不超过16个字")
                {
                    document.getElementById("<%= phDescription1.ClientID%>").value = "";
                }
            }
            function noempty()
            {
                if(document.getElementById("<%= phDescription1.ClientID%>").value == "")
                {
                    document.getElementById("<%= phDescription1.ClientID%>").value = "在这里输入照片标题，不超过16个字";
                }
            }
            
            var imgwh;

            function PreviewImage1()
            {
                var x = document.getElementById('<% = UpImg1.ClientID %>');
                if(x != null)
                {
                    checkupfile(x);
                }
            }
            
            function checkupfile(x)
            {
                if(!x || !x.value) 
                {                         
                    return false;
                }
                var patn = /\.jpg$|\.jpeg$|\.bmp$|\.gif$/i;
                try
                {
                    if(!patn.test(x.value))
                    {            
                        alert("您选择的图片格式不正确，请选择jpg，jepg，gif，bmp格式的图片！");
                        return false;
                    }
                    else
                    {
                        imgwh = new Image();
                        imgwh.src = x.value;
                    }
                }
                catch(e)
                {
                    //alert("您选择文件无法预览，或网络故障无法上传，请稍候再试！");
                    return false;
                }
            }

            function BeforeSaveClick()
            {
                var x = document.getElementById("<% = UpImg1.ClientID %>");

                if(!x || !x.value) 
                { 
                    document.getElementById('<%= Span1.ClientID%>').innerHTML = "请选择要上传的照片。";
                    return false;
                }
                var patn = /\.jpg$|\.jpeg$|\.bmp$|\.gif$/i;
                try
                {
                    if(!patn.test(x.value))
                    {            
                        alert("您选择的图片格式不正确，请选择jpg，jepg，gif，bmp格式的图片！");
                        return false;
                    }
                    else
                    {
                                                
                        var sz = imgwh.width + "x" + imgwh.height;
                        document.getElementById("hidImageWH").value = sz;
                        
                        document.getElementById("hidImageWH_url").value = x.value;
                        return true;
                    }
                }
                catch(e)
                {
                    alert("网络故障无法上传，请稍候再试！");
                    return false;
                }
            }

            </script>