If you get this from your error log, there might be two things you might look into:

1. assets pipeline precompile

2. cache_store is not properly set up for the environment (like staging and production)

To precompile the asset pipeline, you need a Javascript runtime like node.js

Or you will see the error message when you run

rake assets:precompile Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes.

Write the code in /lib/global.rb

def hello; “world”; end

Autoload in /config/application.rb

config.autoload_paths += Dir["#{config.root}/lib/**.rb/"]