Convert Javascript to CoffeeScript (vice versa) directly from vim. Uses js2coffee library.

js2coffeescript.rb

#!/usr/bin/env ruby
require 'tempfile'

file = Tempfile.new(['js2coffee', '.js'])
file.write ARGF.read          # write vim selection to tmp file
file.rewind
file.close
puts `js2coffee #{file.path}` # requires js2coffee
file.unlink                   # deletes the temp file

@gabebw I tried your solution but still got Invalid Token due to the BOM header.
So I modified your solution a bit

#!/usr/bin/env ruby

input = ARGF.read.gsub("\xEF\xBB\xBF", '')
# requires js2coffee
output = `js2coffee <<EOJS\n#{input}\nEOJS`
puts output