Rails custom importmaps snippet

importmaps.rb

Rails::Application.send(:attr_accessor, :importmaps)

module Importmap::CustomImportmapTagsHelper
  def javascript_custom_importmap_tags(name, entry_point: "application")
    importmap = Rails.application.importmaps[name.to_sym]
    return unless importmap

    javascript_importmap_tags(entry_point, importmap: importmap)
  end
end
ActiveSupport.on_load(:action_controller_base) do
  helper Importmap::CustomImportmapTagsHelper
end

class CustomImportmap
  attr_reader :importmap, :name

  def initialize(name, path:, assets_paths: nil)
    @name = name

    importmap_name = name.to_sym
    raise ArgumentError, "Importmap #{importmap_name} already exists" if Rails.application.importmaps&.key?(importmap_name)

    @importmap = Importmap::Map.new
    importmap.draw(path)

    if assets_paths
      importmap.cache_sweeper(watches: assets_paths)
      Rails.application.config.assets.paths += assets_paths
    end

    Rails.application.importmaps ||= {}
    Rails.application.importmaps[importmap_name] = importmap
  end

  def call
    ActiveSupport.on_load(:action_controller_base) do
      before_action { importmap.cache_sweeper.execute_if_updated }
    end
  end

  def erb_usage
    "<%= javascript_custom_importmap_tags(importmap: #{name}) %>"
  end
end