properly yanking word/selection

What is the proper way to yank a word or a selection from a vim script? Right now I'm using
if !bSelection
normal! yaw
else
normal! gvy
endif

but I have some gripes:

1/ yaw (yank a word) yanks the space before the word (some times it doesn't); I don't want the space.
2/ bSelection is needed to tell a function that it was invoked from visual mode; is there a better way?

TIA

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