A Sprockets Engine to write valid JSON in CoffeeScript

coffee_script_json.rb

# The CoffeeScriptJSON module is a Sprockets engine that can be used to write
# JSON files in CoffeeScript.
# 
# This CoffeeScript:
# 
#   # whatever.json.coffee_json
#   hello: 'world!'
# 
# Will be compiled down to:
# 
#   {
#     "hello": 'world!'
#   }
# 
# 
module CoffeeScriptJSON
	class Template < Tilt::CoffeeScriptTemplate

		# Prepares the template. We override `prepare` so we can add the `bare` option
		# to the compilation, to remove the CoffeeScript closure.
		def prepare
			super
			options[:bare] = true
		end

		# Evaluate the template. We override `evaluate` so we can convert the outputted
		# JavaScript into valid JSON.
		def evaluate(scope, locals, &block)
			super
			# (1) Remove the leading and trailing parantheses and semicolon (2) Evaluate as
			# JavaScript to get a Hash (3) Convert it to pretty printed JSON.
			@output = JSON.pretty_generate(ExecJS.eval(@output.gsub(/(\A\(|\);\Z)/, '')))
		end

	end
end

# Register the `CoffeeScriptJSON` engine for the `.coffee_json` file extension.
Rails.application.assets.register_engine '.coffee_json', CoffeeScriptJSON::Template