一个评分控件的错误,请帮忙改正一下
[code=JScript][/code]
<!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>
     <title>无标题页</title>
     <script type="text/javascript">
         function initEvent(){
                var table=document.getElementById("Gread");
                var tds=table.getElementsByTagName("td");
                for(var i=0;i<tds.length;i++){
                     var td=tds[i];
                     td.onclick=changeColor;
                     td.style.cursor="pointer";
                }
         }
         function changeColor(){
            var table=document.getElementById("Gread");
            var tds=table.getElementsByTagName("td");
            var index=indexof(tds,this);
            for(var i=0;i<=index;i++){
                 var td=tds[i];
                 td.style.background="red";
            }
            for(var j=index+1;j<=tds.length;j++){//5个星星时候怎么办
                 var td=tds[i];
                 td.style.background="white";
            }
         }
         function indexof(arry,element){
             for(var i=0;i<arry.length;i++){
                 if(arry[i]==element){
                     return i;
                 }     
             }
         }
     </script>
</head>
<body onload="initEvent()">
<table id="Gread">
     <tr>
         <td>
         ?
         </td>
         <td>
         ?
         </td>         
         <td>
         ?
         </td>
         <td>
         ?
         </td>
         <td>
         ?
         </td>
     </tr>
</table>
</body>
</html>
//Line: 26
//Error: Unable to get value of the property 'style': object is null or undefined(这个是网页的错误提示请问我应该怎么改啊!)
------解决方案--------------------
JScript code
for (var j = index + 1; j <= tds.length; j++) {//5个星星时候怎么办
               var td = tds[i];
               if (i <=4) { td.style.background = "white"; }
               else {return false;}