My immediate guess is that you need to set your variable $$var using that calculation above, not setting $$var to contain a calculation itself. Is there a reason you can't get your jquery code as part of $$var?
the $$var you feed to the webviewer should be fully qualified/readable code, not code that needs additional calculations to complete.
i have to ceck again, problably i already made this test, but following your suggest i should do:
& the field of my xxx.js &
"bla bla >/Html"
yes, you should calculate the FULL code of what you are trying to display in the webviewer using the "Set Variable" script step.
$$Var should only be code, no calculations in it.