Check form before submit - php

Question

The form/table filled with data based on the the status. So the rows in the table are build dynamically.
What i want is that the person who wants to submit the form, has filled in the three fields (STIN / STOUT / REASON) (are dropdown menu's) and the field ITEM must be filled in from the database (not a user input).
If it was one row i think it would be easy, but it depends on the status of an order how many rows it will display and depends on the field ITEM if it has an ITEM.
Example:
Row 1 has the item STIN is selected STOUT is selected REASON is
selected
Row 2 has no item STIN is selected STOUT is selected REASON is
selected
Row two or row 3 with no item must be checked and all the other available rows must be checked when the generate xml button is clicked.
<?php
while ($row = sqlsrv_fetch_array($result)) {
$S1 = $row['Qty_ExchangeStock'];
$S2 = $row['Qty_InService'];
$S3 = $row['Qty_TotalStock'];
$status = '1';
$Stock = $S1 - $S2;
if ($Stock < 1) {
$status = '2';
$Stock = 0;
}
echo '<tr>';
echo '<td><input type="text" name="SONR-'.$counter.'" value="'.$row['No_'].'" size="6" readonly /></td>';
echo '<td><div>'.$row['Brand']. '</div></td>';
echo '<td><div>'.$row['Model']. '</div>';
echo ' <input type="hidden" name="SIGC-'.$counter.'" value="'.$row['Service Item Group Code']. '" /></td>';
echo '<td><input type="text" name="ITEM-'.$counter.'" value="'.$row['Item No_'].'" size="8" readonly /></td>';
echo '<td class="center"><div>'.$Stock. '</div></td>';
echo '<td class="center"><div>'.$row['Claim']. '</div></td>';
echo '<td><input type="text" class="small" maxlength="20" placeholder="Serienummer" name="SNR-'.$counter.'" /></td>';
echo '<td><input type="text" class="small" maxlength="10" placeholder="Approval NR" name="APPNR-'.$counter.'" /></td>';
echo '<td><select id="check" name="STIN-'.$counter.'" class="small">'.$ruilin.'</select></td>';
echo '<td><select name="STOUT-'.$counter.'" class="small">'.$ruiluit.'</select></td>';
echo '<td><select name="REASON-'.$counter.'" class="small">'.$dropdown.'</select></td>';
echo '<td><input type="text" maxlength="70" title="Opmerking: maximaal 80 tekens" name="OPM-'.$counter.'" /></td>';
echo "</tr>\r\n";
$counter++;
}
?>
</tbody>
</table>
<input type="submit" value="Generate XML">
</form>
</div>
</div>
<?php
}
?>

Answer 1

You probably want to start off with server-side validation. The reason is people can turn off validation or use scripting to make calls and you need to be able to validate the logic properly on the server.
In this case you need to define a server-side API (what data does the server have to know?), check and document it. But that starts with design and I don't think you are there yet.
Once you have that done you can add similar checks in Javascript. This improves user experience but it is no replacement for server-side checks.