app/assets/javscripts/application.jsの修正

以下のコードの削除

application.js

//= require_tree .

共通のjavascript配置
common.jsの呼び出し

application.js

//= require common

コントローラ/アクション.js 形式でjavascriptの配置

app/assets/javascripts/top/index.js とか
app/assets/javascripts/top/create.js とか

views/layouts/application.html.erb の修正

<!DOCTYPE html>
<html>
<head>
  <title>TestJs</title>
  <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => true %>
  <%= javascript_include_tag 'application', 'data-turbolinks-track' => true %>
  <%= csrf_meta_tags %>

<%= javascript_include_tag "#{params[:controller]}/#{params[:action]}" if Rails.application.assets.find_asset("#{params[:controller]}/#{params[:action]}.js") %>

</head>
<body>

<%= yield %>

</body>
</html>

config/initializers/assets.rb の追加

Rails.application.config.assets.precompile += %w( top/index2.js )

ページ単位のjavascript読み込み

app/assets/javscripts/application.jsの修正