separate_calendar_bundle.rb

# config/routes.rb
Rails.application.routes.draw do
  get '/calendar', to: 'calendar#index'
  root to: 'home#index'
end

# app/javascript/packs/calendar.js
alert('Calendar loaded')

# app/controllers/calendar_controller.rb
class CalendarController < ApplicationController
end

# app/views/calendars/index.html.erb
<h1>Calendar</h1>
<%= javascript_pack_tag 'calendar' %>