Accessing Form Data From Javascript

I've been using some code to verify form data quite happily, but i've
recently changed the way my form is structured, and I can't get it to work
now.

Originally :

The form is called "form1", and I have selects called "PORTA", "PORTB" ...
etc...

I then had javascript that accessed these selects as below, and it worked
fine.

ind = document.form1.PORTD.selectedIndex;
val = document.form1.PORTD.options[ind].value;
dev = document.form1.PORTD.options[ind].text;


My form is now autogenerated, and form data is stored to file, so I now use
an associative array for thte form elements (so that I can loop through them
easily), The form elements names are now :

McuCfg[PORTA], McuCfg{PORTB} and so on

Now, I modified the javascript so that it now uses the McuCfg[] associative
array :

ind = document.form1.McuCfg[PORTD].selectedIndex;
val = document.form1.McuCfg[PORTD].options[ind].value;
dev = document.form1.McuCfg[PORTD].options[ind].text;

When the script runs, I get the error

"document.form1.McuCfg.PORTD is null or not an object"

I have used the same notation that i know works for the "options" array
although that's not an associative array.