เขียน script ตรวจสอบค่าที่จะเติมลงใน text box อย่างไรครับ

<script language="javascript">
		function fncchk(){
				var a1= document.frm1.a1.value;
				var a2= document.frm1.a2.value;
				if(a1 < a2){
						alert('คุณระบุจำนวนเกินกำหนด');
						document.frm1.a2.value="";
						document.frm1.a2.focus();
						return false; 						
				}

		}
</script>
<form name="frm1" action="#" method="post" >
<input name="a1" type="text" id="a1" value="3"  />
<input name="a2" type="text" id="a2" onkeyup="JavaScript:fncchk();"/>
</form>

<form name="stockoutdata" action="save_stockoutdata.php" method="post">
$sql_invoice="select b.*,e.* from str_bill b, str_equipment e where e.eqm_id=b.eqm_id and b.bill2='$billno' order by b.set_id desc ";
	$query_invoice=mysql_db_query($db,$sql_invoice);
	if($num_invoice==0){
		echo "ยังไม่มีรายการส่งของ";
	}else{
	echo "<table width='55%' cellpadding='0' cellspacing='0' border=1 bordercolor='#FFFFFF'>
			<tr height='25' class='style6'>
			 <td width='8%' align='center'>ลำดับ</td>
			 <td width='42%' align='center'>รายการ</td>
			 <td width='10%' align='center'>จำนวนเบิก</td>
		     <td width='20%' align='center'>จำนวนจ่าย</td>
		     <td width='20%' align='center'>MFG.Date</td>
		    </tr>";
	while ($rs_invoice=mysql_fetch_array($query_invoice)){
	  $mfg = $rs_invoice[eqm_date];
	  $set_amount = $rs_invoice[set_amount];
	  $eqm_exp = $rs_invoice[eqm_expire];
	  $qmid =$rs_invoice[eqm_id];
	 list($y,$m,$d)=explode('-',$mfg);
	 $exp = Date("Y-m-d", mktime(0,0,0,$m,$d+$eqm_exp,$y));

	// $exp = date('Y-m-d', strtotime('+$eqm_exp day', strtotime($mfg)));
	 $bgc = ($bgc=="") ? "#FFFFF" : "";
      echo "<tr height='25' bgcolor='$bgc' class='style7'>
			 <td align='center'>$q</td>
			 <td>&nbsp;$rs_invoice[eqm_name]</td>
			 <td align='center'>$set_amount</td>
			 <td align='center'><input type='text' name='stock_out[]' size='2' maxlength='3' onkeypress='check_number()' ></td>";
			 
			 ?>
			 <td align='center'><input type="text" name="date_mfg[]"  id="dateInput<?echo $q?>" /></td> 
			 <input type="hidden" name="qmid[]" value="<?=$qmid?>" />
	         <input type="hidden" name="set_amount[]" value="<?=$set_amount?>" />
<?	echo "</tr>";
       $q++;
	}
			
	echo "</table><p>";
	
	?>
	  <input type="button" name="button" value="บันทึก"  onclick="javascript: document.stockoutdata.submit();" />
&nbsp;&nbsp;&nbsp;&nbsp;
      <input type="button" name="button" value="ยกเลิก"  onclick="javascript: document.stockoutdata.reset();" />
    </label></td>
	  
	  <input type="hidden" name="billno" value="<?=$billno?>" />
	<?
	}
	?>
   </td>
  
  </tr>
 </table>
 </form>

<form name="stockoutdata" action="save_stockoutdata.php" method="post">
$sql_invoice="select b.*,e.* from str_bill b, str_equipment e where e.eqm_id=b.eqm_id and b.bill2='$billno' order by b.set_id desc ";
$query_invoice=mysql_db_query($db,$sql_invoice);
if($num_invoice==0){
echo "ยังไม่มีรายการส่งของ";
}else{
echo "<table width='55%' cellpadding='0' cellspacing='0' border=1 bordercolor='#FFFFFF'>
<tr height='25' class='style6'>
<td width='8%' align='center'>ลำดับ</td>
<td width='42%' align='center'>รายการ</td>
<td width='10%' align='center'>จำนวนเบิก</td>
<td width='20%' align='center'>จำนวนจ่าย</td>
<td width='20%' align='center'>MFG.Date</td>
</tr>";
while ($rs_invoice=mysql_fetch_array($query_invoice)){
$mfg = $rs_invoice[eqm_date];
$set_amount = $rs_invoice[set_amount];
$eqm_exp = $rs_invoice[eqm_expire];
$qmid =$rs_invoice[eqm_id];
list($y,$m,$d)=explode('-',$mfg);
$exp = Date("Y-m-d", mktime(0,0,0,$m,$d+$eqm_exp,$y));

// $exp = date('Y-m-d', strtotime('+$eqm_exp day', strtotime($mfg)));
$bgc = ($bgc=="") ? "#FFFFF" : "";
echo "<tr height='25' bgcolor='$bgc' class='style7'>
<td align='center'>$q</td>
<td>&nbsp;$rs_invoice[eqm_name]</td>
<td align='center'>$set_amount</td>
<td align='center'><input type='text' name='stock_out[]' size='2' maxlength='3' onkeypress='check_number()' class='stockout' /></td>";

?>
<td align='center'><input type="text" name="date_mfg[]" id="dateInput<?echo $q?>" /></td>
<input type="hidden" name="qmid[]" value="<?=$qmid?>" />
<input type="hidden" name="set_amount[]" value="<?=$set_amount?>" />
<? echo "</tr>";
$q++;
}

echo "</table><p>";

?>
<input type="button" name="button" value="บันทึก" onclick="javascript: document.stockoutdata.submit();" />
&nbsp;&nbsp;&nbsp;&nbsp;
<input type="button" name="button" value="ยกเลิก" onclick="javascript: document.stockoutdata.reset();" />
</label></td>

<input type="hidden" name="billno" value="<?=$billno?>" />
<?
}
?>
</td>

</tr>
</table>
</form>
  <script src="http://code.jquery.com/jquery-latest.js"></script>
  <script type="text/javascript">
	$(document).ready(function() {
		$("input.stockout").keydown(function(){
			var maximum = $(this).parent().prev().text();
			if($(this).val() <= maximum)
				return true;
			else 
				$(this).val(maximum);
		});
	});
  </script>