update field in form after dropdown and button

[Wroblewski]

Hi,

Joomla! 2.5.6, Fabrik 3.0.6

I have got two tables:

desc1:
id - internalid,
tmpid - databasejoin to desc_tmp.tmpid,
copy_from_tmp - button,
desc - text)

and desc_tmp :
(tmpid - internaid,
tmp_desc - text)

with foreign key desc1.tmpid=desc_tmp.tmpid

User action: dropdown and choose tmpid, click button 'copy_from_tmp' and copy tmp_desc to desc by clicking button. My JS in button (on Click) is:
$('desc1___desc').value = $('desc_tmp___tmp_desc').getValue() ;
but it does not work.

How to get tmp_desc after?

Thanks
Grzegorz