Transform Map run script syntax won't work in onAfter/onBefore ?

[Nolan4]

The syntax --> target.city = source.u_city + "(" + source.u_state + ")"; works in run script of a transform map but when I try to run the same syntax through onBefore or onAfter it doesn't work. 

My question is, is the syntax a bit different in Transform scripts(onBefore or onAfter) than it is in Run script ? i.e. do we need to add any update code? 

I had also tried  if (action == 'insert') {
target.city = source.u_city + "(" + source.u_state + ")";
} 

but didn't work. Please suggest, thanks.

[Rahul91]

you can use the field script to set the values. But not sure on why it does not set the values directly form on Before or on After.