You must include all the js / css files that you add to the methods #javascript_include_tag
and #stylesheet_link_tag
to the array Rails.application.config.assets.precompile
. Check config/initializers/assets.rb
(create if it does not exist). Here's how it should look:
Rails.application.config.assets.precompile += %w( login.js )
Restart the Rails server after editing.
By the way, this is self-evident from the error text.
Rails Assets Pipeline: http://guides.rubyonrails.org/asset_pipeline.html.