点击单选按钮弹出登录框问题
有一组单选按钮   ,点击“是”在下面出现登录框。点击否不出现。但是如果我不断的点击“是”他就会不断的出现登录框。怎么解决?   
 代码如下:     
  <style>    
 div#blocks{ 
 color:#CCCC33;margin-left:10px; 
 margin-top:5px; 
 font-size:12px;} 
 div#blocks   input{width:60px; 
 height:16px;} 
  </style>    
  <script   langage= "javascipt ">    
 function   showbar(objtt){   
 var   divnode=document.createElement( "DIV "); 
             divnode.id= "blocks "; 
 var   spannode_a=document.createElement( "SPAN ");               
 var   login=document.createTextNode( "用户名 ");            
 var   area_a=document.createElement( "INPUT "); 
             area_a.id= "input_a "; 
                      area_a.type= "text "; 
 var   spannode_b=document.createElement( "SPAN ");               
 var   passwords=document.createTextNode( "密码 "); 
 var   area_b=document.createElement( "INPUT "); 
          area_b.id= "input_b ";    
          area_b.type= "password "; 
          divnode.appendChild(spannode_a); 
                      spannode_a.appendChild(login); 
                      divnode.appendChild(area_a); 
                      divnode.appendChild(spannode_b); 
                      spannode_b.appendChild(passwords); 
                      divnode.appendChild(area_b); 
 objtt.appendChild(divnode);                        
 } 
  </script>      
  </head>    
  <body   id= "myBody ">  
  <h2> 插入表格 </h2>  
  <hr>  
 是 <input   name= "aa "   type= "radio "   onclick= "showbar(myBody) ">  
 否 <input   name= "aa "   type= "radio ">  
        <br>  
  </body>      
------解决方案--------------------办法很多 
  <style>    
 div#blocks{ 
 color:#CCCC33;margin-left:10px; 
 margin-top:5px; 
 font-size:12px;} 
 div#blocks input{width:60px; 
 height:16px;} 
  </style>    
  <script langage= "javascipt ">  
 var isok=false 
 function showbar(objtt){ 
 if(isok) return  
 var divnode=document.createElement( "DIV "); 
     divnode.id= "blocks "; 
 var spannode_a=document.createElement( "SPAN ");       
 var login=document.createTextNode( "用户名 ");      
 var area_a=document.createElement( "INPUT "); 
     area_a.id= "input_a "; 
        area_a.type= "text "; 
 var spannode_b=document.createElement( "SPAN ");       
 var passwords=document.createTextNode( "密码 "); 
 var area_b=document.createElement( "INPUT "); 
    area_b.id= "input_b ";  
    area_b.type= "password "; 
    divnode.appendChild(spannode_a); 
        spannode_a.appendChild(login); 
        divnode.appendChild(area_a); 
        divnode.appendChild(spannode_b); 
        spannode_b.appendChild(passwords); 
        divnode.appendChild(area_b); 
 o