Not quite there yet, I think 
At the moment following a //JavaScript line with JS values other than string literals returns either undefined or puzzling URL-encoded strings, which is:
- encouraging (certainly a sign of some JS evaluation going on)
- not yet usable, I think, the expected string return mechanism is unclear (and there seems to be a missing urlDecode phase)
\\JavaScript
"hello" + "there"
→ hellothere
which seems a good start, but then
\\JavaScript
Application("Finder").name()
→ undefined
and least predictably of all:
this
→ %5Bobject%20GlobalObject%5D
Which suggests an opacity or slight oversight at some point in the process.
It will be very useful when it settles down, though.
PS a clue to some kind urlencode ⇄ urldecode gap is suggested by the fact that:
\\JavaScript
"hello there"
→ hello%20there