留言板回复内容修改问题，急啊~~

Question

<textarea cols="80" name="content" rows="20" wrap="VIRTUAL" style="font-size: 13">
</textarea>                                                  
                                                                                         
<input TYPE="button" VALUE="加粗字体"  onclick="addBold(document.forms[0].content)"> 
<input TYPE="button" VALUE="加大字体"  onclick="addBig(document.forms[0].content)">       
<script language=javascript>function addBold(tbox)
  {
   var selstr; 
   tbox.focus();
   selstr=document.selection.createRange().text;
   if (selstr!='')
      {
       document.selection.createRange().text="<B>" + selstr + "</B>";
      } 
  }
  
  
  
  function addBig(tbox)
  {
   var selstr; 
   tbox.focus();
   selstr=document.selection.createRange().text;
   if (selstr!='')
      {
       document.selection.createRange().text="<big>" + selstr + "</big>";
      } 
  }
</script>

Answer 1

不对的哦，点击的时候提示 'undefined' 为空或不是对象的错误

Answer 2

<form name="ff">
<textarea cols="80" name="content" rows="20" wrap="VIRTUAL" style="font-size: 13">
</textarea> 
</form>