form提交判断问题！

<script language="JavaScript">
function toSubmit(){
    if(form1.username.value==""){
 alert("用户名不能为空！");
 return false;}
 if(form1.password.value==""||form1.repassword.value==""){
  alert("密码框不能为空！");
  return false;
 }
 
 if(form1.password.value!=form1.repassword.value){
  alert("两次输入的密码不一致，请确认后重新输入");
  return false;
 }
 else{return true;}
 
 
}

<form name="form1" action="tjuser.asp" method="post" target="hideFrame">
<table width="600" border="0" cellpadding="0" cellspacing="0">
  <!--DWLayoutTable-->
  <tr>
    <td height="25" colspan="2" valign="middle" class="title">添加下载用户</td>
  </tr>
  <tr>
    <td width="80" height="25" valign="middle">用户名</td>
    <td width="520" valign="middle"><input name="username" type="text" id="username" size="20"></td>
  </tr>
  <tr>
    <td width="80" height="25" valign="middle">新密码</td>
    <td width="520" valign="middle"><input name="password" type="password" id="password" size="20"></td>
  </tr>
  <tr>
    <td height="25" valign="middle">确认新密码</td>
    <td valign="middle"><input name="repassword" type="password" id="repassword" size="20"></td>
  </tr>
  <tr>
    <td height="40">&nbsp;</td>
    <td valign="middle"><input type="submit" name="Submit" value="添加用户" class="button" onclick="return toSubmit();">
    </td>
  </tr>
</table>
</form>