อยากจะใช้ Javascript ตรวจสอบข้อมูลในฟังก์ชัน If อะครับ

if($_POST["hdnCmd"] == "Add")
{		
	if($_POST["Rec_Id"]!='' && $_POST["Drg_Id"]!='' && $_POST["Price_Sale"]!='' && $_POST["Drg_Qtt"]!='' 
	&& $_POST["Total"]!='' && $_POST["Drg_Barcode"]!=''){
	
	
	
$dateyear = date(Y);
$datemonth = date(m);
$dateday = date(d);
$sqlDetail8 = "SELECT * FROM store WHERE Drg_Barcode = '".$_POST["Drg_Barcode"]."' && No >= '".$_POST["No"]."' && Drg_Qtttotal >= '".$_POST["Drg_Qtt"]."' && Drg_Exp >= '".$dateyear.-$datemonth.-$dateday."' ORDER BY DATEDIFF(Drg_Exp,'".$dateyear.-$datemonth.-$dateday."') ASC LIMIT 0 ,1 ";



$rs8 = mysql_query($sqlDetail8);

$row8 = mysql_fetch_array($rs8);
$Date = $row8['Date'];
$Drg_Expday = $row8['Drg_Expday'];
$Drg_Expmonth = $row8['Drg_Expmonth'];
$Drg_Expyear = $row8['Drg_Expyear'];
$Drg_Qtttotala = $row8['Drg_Qtttotal'];
$No = $row8['No'];	
$Drg_Qtttotala;

$Drg_Qtt = $_POST["Drg_Qtt"];
$Drg_Qtttotal = $Drg_Qtttotala - $Drg_Qtt;
	if($Drg_Qtttotala >= $_POST["Drg_Qtt"]){
	
	
	$strSQL2 = "INSERT INTO sale_log ";
	$strSQL2 .="(Rec_Id, Drg_Id, Price_Sale, Drg_Qtt, Total, No) ";
	$strSQL2 .="VALUES ";
	$strSQL2 .="('".$_POST["Rec_Id"]."','".$_POST["Drg_Id"]."','".$_POST["Price_Sale"]."' ";
	$strSQL2 .=",'".$_POST["Drg_Qtt"]."' ";
	$strSQL2 .=",'".$_POST["Total"]."','".$No."') ";
	$objQuery2 = mysql_query($strSQL2);
	if(!$objQuery2)
	{
		echo "มีข้อผิดพลาดเกิดขึ้น/กรุณากลับไปเพิ่มข้อมูลใหม่ [".mysql_error()."]";
	}
	
	
	if($objQuery2 || $rs8){
	$strSQL3 = "UPDATE store SET Drg_Qtttotal = '$Drg_Qtttotal' WHERE Date = '$Date' && No = '$No' && Drg_Expday = '$Drg_Expday' && Drg_Expmonth = '$Drg_Expmonth' && Drg_Expyear = '$Drg_Expyear' && Drg_Barcode = '".$_POST["Drg_Barcode"]."'";
	$objQuery3 = mysql_query($strSQL3);
	if(!$objQuery3)
	{
		echo "Error Save [".mysql_error()."]";
	}
	
	
	


	$strSQL4 = "UPDATE stock SET Drg_Qtttotal = '$Drg_Qtttotal' WHERE Drg_Exp = '$Drg_Expyear-$Drg_Expmonth-$Drg_Expday' && Drg_Barcode = '".$_POST["Drg_Barcode"]."'";
	$objQuery4 = mysql_query($strSQL4);
	if(!$objQuery4)
	{
		echo "Error Save [".mysql_error()."]";
	}
	
	
	
	
	
	
	
	}
	}else{             //ในส่วนนี้อยากจะตรวจสอบโดยใช้ Javascript อะครับ
		echo จำนวนซื้อมากกว่าที่มีอยู่;
		}
	


}else{        //ในส่วนนี้อยากจะตรวจสอบโดยใช้ Javascript อะครับ
	echo กรุณาใส่ข้อความให้ครบถ้วน;
	}
}