select制御表示隠し

<script>  
  function   setChange()  
  {  
  if   (document.f.selfs.value   ==   "1")    
  {                          
  tb1.style.display   =   "block";                  
  }                  
  else    
  {                          
      tb1.style.display   =   "none";                  
  }  
                    if   (document.f.selfs.value   ==   "2")    
  {                          
  tb2.style.display   =   "block";                  
  }                  
  else    
  {                          
      tb2.style.display   =   "none";                  
  }        
  }  
   
  </script>  
  <form   name=f>  
   
  <select   name="selfs"   size="1   onchange="setChange()">  
      <option   selected>    </option>  
      <option   value="1">  1</option>  
      <option   value="2">  2</option>  
  </select>  
   
   
  <table   id='tb1'   style='DISPLAY:none'>  
    1       1       1  
  </table>    
   
  <table   id='tb2'   style='DISPLAY:none'>  
    2     2     2  
  </table>  
  </form>