server.rb

require 'pathname'
require 'sinatra'
require 'sass'
require 'babel/transpiler'

Sass.load_paths << File.expand_path('bower_components/bibi/bibi-dev/res/styles/src', __dir__)

configure do
  set :app_file, File.expand_path('.')
end

not_found do
  'Not Found'
end

before do
  # headers 'Content-Security-Policy' => "script-src 'self'"
  headers 'Access-Control-Allow-Origin' => '*'
  headers 'X-Frame-Options' => 'ALLOWALL'
  path = File.join(settings.app_file, clean_path_info(unescape(request.path_info)))
  @path = Pathname(path)
  halt 404 unless @path.file?
end

get '/src/*.js' do
  content_type 'application/javascript'
  Babel::Transpiler.transform(@path.read)['code']
end

get '/*.html' do
  erb @path.read
end

get '/*' do
  content_type mime_type(@path.extname)
  @path.open
end