JS 问题，求解决 人在线！


问题描述：选中改行，改行颜色变灰。选中后点击修改按钮就会提交。。
但是我不选中的话，点击查修改按钮也会提交。我就是想，如果没选中的话，就不执行提交操作。
<input type="button" value="修改" style="width:50px; height:40px;" onclick="javascript:window.open(reurl3(),'_self')"/>
<html xmlns="http://www.w3.org/1999/xhtml">
<head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>湖南建工目标成本管理系统</title>
<style type="text/css">
body{text-align:center; font-size:14px; margin:0 auto; width:1024px;height:768px;  }
#mainFrame{height:768px; width:1024px; margin:0 auto;padding:0px;}
 #head{height:120px;width:1024px;border:#666 1px solid;}

 #rightFrame{ height:648px; width:1024px;  margin: 0px;padding:0px; float:left;border:#666 1px solid; }
.clearfloat { /* 此类应当放在 div 或 break 元素上，而且该元素应当是完全包含浮动的容器关闭之前的最后一个元素 */
clear:both;
    height:0;
    font-size: 1px;
    line-height: 0px;
}
</style><script type="text/javascript">
  var currentActiveRow;   
  function changeActiveRow(obj)   
  {   
  if(currentActiveRow)   
    currentActiveRow.style.backgroundColor="";   
    currentActiveRow=obj;   
    currentActiveRow.style.backgroundColor="#dddddd";   
  }   
  
    var key = 0;
    var flag = false;
    var b='a';
 function selectTable() {
  var table = document.getElementById("table");
  var rows = table.rows.length;
 
  for(var i=0;i<rows;i++) {
  var row = table.rows[i];
  if(row.style.backgroundColor == "#dddddd") {
    key = row.cells[0].innerHTML; 
     flag = true;
    break ;
  }
  }
  if(!table.rows[i]){
  alert("请选择您要操作的记录!");
  flag = false;
    }
     
  }
 
   function test(){
   selectTable();
    if(flag == false) {
      return;
    } else {
    
     //alert('选中的行为：' + key);
     return key;
     
     }

}







function reurl()
{
     var a=test();
 var b='./project.do?method=delete&billno='+a;
    // alert(b);
    if(a=undefined)
     {
     return ;
     }
      return b;
     
}


function reurl2()
{
  var c=test();
  var d='./project.do?method=findkey&billno='+c;
  if(c=undefined)
  {
  return ;
  }
  return d;

}


function reurl3()
{
  var e=test();
  var f="./project.do?method=xiugaiyemian&billno="+e;
  if(e=undefined)
  {
    return ;
  }
  return f;
  
}   </script></head><body><!--最外层框架 -->
    <div id="mainFrame">
        
        <!--头部框架 -->
     <div id="head">
      <table border="0" cellpadding="0" cellspacing="0" width="100%" height="100%">
        <tr>
         <td width="13%" height="18">
            
            </td>
            <td width="60%">
            
        </td>
            <td width="27%">
            
            </td>
        </tr>
        <tr>
         <td height="101" align="center">
             <img src="WebRoot/images/logo.jpg"/>
            </td>
            <td align="left">
             <font color="#000000" style="font-size:48px" face="华文彩云">湖南建工目标成本管理系统</font>
            </td>
            <td>
            
            </td>
        </tr>
        <tr>
         <td>
            
            </td>
            <td>
            
            </td>
            <td>
            
            </td>
        </tr>
       </table>        
     </div><!--头部框架结束 -->
        <!--右部框架 -->
        <div id="rightFrame">
          <div style=" width:100%; height:70px;">
         <div style="margin-left:25px; height:40px; width:95%; margin-top:20px;">
            <table width="100%" height="100%" cellpadding="0" cellspacing="0" border="0">
                     <tr>
                         <td width="84%">
                             <input type="button" value="查看" style="width:50px; height:40px;" onclick="javascript:window.open(reurl2(),'_self')"/>
             <input type="button" value="新增" style="width:50px; height:40px;" onclick="javascript:window.open('./project.do?method=tianjiayemian','_self')"/>
                 <input type="button" value="修改" style="width:50px; height:40px;" onclick="javascript:window.open(reurl3(),'_self')"/>
                 <input type="button" value="删除" style="width:50px; height:40px;" onclick="javascript:window.open(reurl(),'_self')"/>
                                <input type="button" value="查询" style="width:50px; height:40px;" onclick="javascript:window.open('./project.do?method=queryindex','_self')"/>
                                <input type="button" value="核算科目设置" style="width:70px; height:40px;" onclick="javascript:window.open('...','_self')"/>
                 </td>
                            <td width="8%"></td>
                            <td width="8%">
                             <input type="button" value="退出" style="width:50px; height:40px;"/>
                            </td>
                        </tr>
                    </table>
            </div>
        </div>
        <div style="width:100%; height:5px;"><hr/></div>
        
         <div
style="width: 95%; height: 430px; font-size: 12px; overflow: auto; margin:0 auto;">
  <table width="100%" border="1" cellpadding="0" bordercolor="#666666"
cellspacing="0" id="table">
<tr class="scrollColThead">
<th height="30" align="center" width="83">
项目编码
                        </th>
<th width="345" align="center" >
   项目名称
                        </th>
                        <th width="202" align="center" >
经营单位
</th>
                        <th width="131" align="center" >
项目状态
                        </th>
                        <th width="199" align="center" >
签订日期
                        </th>
</tr>
                    
                    
                     <c:forEach items="${list}" var="l">   
       
       <tr onClick="changeActiveRow(this)">
<td height="30">
${l.billno}
</td>
<td >
${l.name}
</td>
                        <td>
${l.epsno}
</td>
<td>
${l.billstatus}
</td>
                        <td>
${l.filldate}
</td>
           
    </tr>  
   
    </c:forEach>  
                    
                    
                    


</table>
</div>
        </div>  <!--右部框架结束 -->
        <br class="clearfloat"/>
 
    </div><!--最外层框架结束 -->
 
</body>
</html>