页面提交的问题？？？问下高手此问题如何解决

Question

<script type="text/javascript">
function check()
{
   if(document.all.user_name.value=='')
   {
       alert("用户名不能为空");
       document.all.user_name.focus();
       return false;
   }
   return true;
}
</script><form name="form1" post="confirm.php" onsubmit="return check();">
<input type="text" name="user_name">
<input type="submit" name="submit">
</form>

Answer 1

<script type="text/javascript">
function check()
{
   if(user_name.value=="")
    return false;
}
</script><form name="form1" post="confirm.php" onsubmit="return check();">
<input type="submit" name="submit">呵呵</form>

Answer 2

<script type="text/javascript">
function check(obj)
{
   if(!obj.user_name.value)
   return false;
}
</script><form name="form1" post="confirm.php" onsubmit="return check(this);">
<input type="submit" name="submit"></form>