[jQuery] How can the keypress characters be modified?

[simunaqv]

Hello,
I am trying to modify character codes in a textarea inside the
keypress handler as shown in the following:

$('textarea[name=message]').keypress( function(e)
        {
            var whichChar = String.fromCharCode(e.which);
                        e.which= codes[whichChar];
        }
      );

Here codes is a lookup table. I have also tried modifying the keyCode
attribute of the event but it is not working. This method of modifying
key codes is working fine otherwise but when used with jquery, it is
does not seem to work. Is there something that I am missing?