[web2py] powertable | insert JSFUNCTION in dtfeatures['fnFooterCallback']

[palomar]

Hi,
I'm using the plugin powertable and I need to insert my JS funciont on the 
footer; the option to change is 
dtfeatures['fnFooterCallback']
but I have a problem to insert my JS function.
What or where I have to insert it?
Thanks...
 

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