Controllo text di un vettore in JS

[kekkosf]

Ho generato la seguente form

<form action = "f4_reg_pre.php" METHOD = "POST" NAME = "F4" OnSubmit="form_val('F4');return false;">
                 <INPUT TYPE = "Hidden" Name = "dati" Value = "kekko">
                 <INPUT TYPE = "Hidden" Name = "azi" Value = "203">
                 <INPUT TYPE = "Hidden" Name = "uni" Value = "01">
                 <INPUT TYPE = "Hidden" Name = "lm" Value = "1">
                 <INPUT TYPE = "Hidden" Name = "mat" Value = "0025">
                 <INPUT TYPE = "Hidden" Name = "Mese" Value = "09">
                 <INPUT TYPE = "Hidden" Name = "Anno" Value = "2007">
                 <INPUT TYPE = "Hidden" Name = "User" Value = "cl_kekko1">

                 <table width = "90%" align = "center" border = "1" cellspacing = "0" cellpadding = "1">
                        <tr bgcolor = "blue">
                            <th><FONT FACE = "Verdana" SIZE = "2" Color = "yellow">Dal</th>
                            <th><FONT FACE = "Verdana" SIZE = "2" Color = "yellow">Al</th>
                            <th colspan="2"><FONT FACE = "Verdana" SIZE = "2" Color = "yellow">Causale</th>
                            <th><FONT FACE = "Verdana" SIZE = "2" Color = "yellow">Ore</th>
                            <th><FONT FACE = "Verdana" SIZE = "2" Color = "yellow">Test</th>
                        </tr>
                        <tr>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Dal[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Al[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG1</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG1[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG1[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG1[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr>
                   <tr>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG2</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG2[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG2[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG2[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr><tr>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Dal[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Al[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG1</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG1[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG1[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG1[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr>
                   <tr>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG2</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG2[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG2[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG2[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr><tr>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Dal[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center" rowspan="2">
                            <INPUT TYPE="Text" Name="Al[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG1</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG1[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG1[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG1[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr>
                   <tr>
                        <td align = "center"><FONT FACE = "Verdana" SIZE = "2">CG2</FONT></td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="CG2[]" Value="" SIZE="4" MAXLENGTH="2"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <INPUT TYPE="Text" Name="OG2[]" Value="0.00" SIZE="6" MAXLENGTH="5"
                                   style = "background:#CCCCCC; font-family:Verdana; font-size:9pt">
                        </td>
                        <td align = "center">
                            <SELECT SIZE="1" NAME="TG2[]" style = "background:#CCCCCC;font-family: Verdana; font-size: 9pt">
                                    <Option Value = "S">In Sostituzione</OPTION>
                                    <Option Value = "A">In Aggiunta</OPTION>
                                    <Option Value = "R">Ripristino Ordinarie</OPTION>
                            </SELECT>
                        </td>
                   </tr>
                        <tr>
                             <td align = "center" colspan = "6">
                                 <INPUT TYPE = "Submit" Value = "Elabora">
                             </td>
                        </tr>
                 </table>
           </form>

Adesso dovrei generare la funzione JS form_val, che mi dovrebbe effettuare dei controlli sui campi. Come faccio a catturare il valore di TG2[1] o CG2[2] ecc. ecc. ?
Calcolando che la lunghezza del vettore non la so a monte ?

[kekkosf]

         function form_val(nome_form, lunghezza_vettore)
         {
                  for (i = 0; i < lunghezza_vettore; i++)
                  {
                       campoDal = "Dal["+i+"]";
                       campoAl = "Al["+i+"]";
                       Dal = document.forms[nome_form].elements[campoDal].value;
                       Al = document.forms[nome_form].elements[campoAl].value;

                       if (Dal > Al)
                       {
                           alert('Data Incoerente');
                           return false;
                       }
                       else
                       {
                           alert ('Ok');
                           return false;
                       }
                  }

         }

Chiaramente nell'OnSubmit del form, va messo il secondo parametro